WHEN Rita Jeptoo defended her Chicago Marathon title last month, the $100,000 prize money was almost incidental.

With her victory in Boston as defending champion earlier this year - the third of her career there, and worth $150,000 in prize money - it confirmed a $500,000 bonus for the World Marathon Majors title.

She is only the second woman to have won both Boston and Chicago back to back and has been under 2:20 on both courses, neither known to be fast. Only three women, including Paula Radcliffe, have ever gone faster, and she is the most durable of them.

Over the past decade, Jeptoo has won in Stockholm, Milan and Eldoret. She has been in the top five in Rotterdam, Frankfurt, New York and Turin. Indeed, in 19 marathons her worst placing was seventh (twice) in two World Championships.She has won many other, shorter races, with significant prize money.

Her best time is 2:18.47, in Boston this year. With participation money (likely to be in excess of $100,000) and bonuses from her kit sponsor, this year's double would have earned her in excess of $1m, but for one thing. She has failed a dope test for blood-boosting erythropoeitin.

This is not just bad news for the 33-year-old Jeptoo, but for the credibility of Kenyan endurance running, increasingly racked by allegations of doping.

Yesterday, despite her manager having stated earlier that she would not challenge the A sample's findings, she asked for the B sample to be tested. This is her right, but it's exceedingly rare for the second test to contradict the first, and under strict doping protocol her identity should have remained secret pending confirmation.

The World Marathon Majors withheld the $500,000 prize on Sunday and she was provisionally suspended yesterday by the Kenyan authorities.

Last year, Kenyan men won 79 of 131 marathons worldwide. Their women won 47 out of 133. It's a staggeringly disproportionate influence for a relatively small nation, and more disproportionate if one considers that Kenya's endurance runners come from a tiny fraction of that country's population.

Cynics - and they include Kenya's three-time world steeplechase champion, Moses Kiptanui - suggest doping is at the back of it.

Endurance running is a major industry for Kenya. Conservatively, Jeptoo can be judged to have earned upwards of $3m during her career. When one considers this in the light of the average annual wage of a subsistence farmer where she comes from (perhaps $500 a year), $3m equates to something close to 6000 years' annual income.

The surprise is not that some people cheat, but that the rewards do not tempt more Kenyans and those of similar natural aptitude and native environment in Ethiopia and Eritrea to do so.

A total of 36 Kenyan athletes have failed tests in the past two years, but the International Association of Athletic Federations, as of last week, lists just 10 of them as serving a suspension. Only two of these are for erythropoeitin, which boosts the red-cell count and the oxygen-carrying capacity of the blood.

It is the illegal performance booster of choice for endurance athletes and was at the centre of the Festina affair in the Tour de France, which all but destroyed professional road cycling. The IAAF catalogue of athletics offenders contains not a single Ethiopian or Eritrean, the two other nations which, with Kenya, have had the biggest impact on endurance running in recent years.

That hardly hints at an EPO explosion in East Africa. I'm told by medical people who know about such matters that EPO dosages required to sustain a structured doping camapign would cost upwards of £10,000 per year.

That's hardly a sum within the grasp of an aspiring Kenyan runner. Many of them can't afford a pair of running shoes. However, it's little more than pocket money for a serial marathon winner.

Marion Jones, the multiple Olympic champion, was the highest-earning female to be implicated in EPO doping, but Jeptoo would be the highest-earning endurance runner. If convicted it would tear the fragile fabric of the sport and place a huge question mark over the validity of outstanding Kenyan performances and achievements.

This will surely further irk the likes of Kiptanui, first man to break eight minutes for the 3000m 'chase.

The worst doping offender is Russia (67 currently suspended), followed by Turkey (44) and India (38). Jamaica, over whose sprint prowess there has been so much speculation, has four athletes currently suspended. Ukraine has 15, the US and Belarus 12 each, and Romania eight.

The World Anti-Doping Agency criticised the Kenyan athletics authorities for insufficient rigour in their test procedures, and the IAAF responded by increasing in and out-of-competition tests on Kenyans - now more than 700 a year, the majority out of competition.

Jeptoo tested positive from a sample taken in Kenya two weeks before the Chicago race. Athletics can ill-afford to have the integrity of marathon running tarnished, and the IAAF can take credit for acting. Even less can they afford the kind of freefall decline into which cycling was plunged by EPO.

Jeptoo may not be a household name like Jones, but she is a significant figure - a big earner and the highest-profile female doping capture since Jones went down.

And, unlike the American, she has been caught by the sport's initiatives - not by the US justice system.