In one of Scotland's biggest health board areas, the number of doctors and consultants on duty fell from nearly 1200 on weekdays to just 25 at weekends. The number of consultants in another area fell from 210 on an average weekday to seven at weekends.
The figures, obtained by Scottish Labour, prompted warnings about the level of services available at weekend and brought renewed calls for a comprehensive review of staffing levels.
The health board figures showed a fall in medical staff at NHS Lothian from 1182 on weekdays to 25 at weekends. The number of nurses fell from 5186 to 1919.
Staffing in other fields also fell, with staff such as dieticians, physiotherapists, speech and language therapists and occupational therapists dropping from 1853 to 90.
The falls were mirrored in figures from Forth Valley and Fife health board areas, which also responded to the Freedom of Information request.
The number of consultants in Fife fell from 210 on an average weekday to seven at weekends, while nurse numbers dropped from 2043 to 648. In Forth Valley, consultants and doctors fell from 356 to 57, and nurses from 2251 to 1111.
Johann Lamont, the Scottish Labour leader, called on First Minister Alex Salmond to order a full-scale review of staffing levels, saying the figures highlighted a serious problem delivering adequate care. She told MSPs: "The British Medical Association says that the situation is unsustainable and the Royal College of Nurses is calling for a full review.
"Those calls are backed by The Herald newspaper, which is leading calls for an honest debate.
"Is the First Minister prepared to get beyond crisis management and agree to a full-scale review of NHS staffing and resources?"
Mr Salmond insisted the NHS did not need a review and said overall staffing levels had risen, but Ms Lamont's call was backed by the Royal College of Nursing.
Its Scotland director, Theresa Fyffe, said: "We fully support the need for proper seven-day working in the NHS but we really need a top-to-bottom review of the whole system of how services are staffed and resourced.
"The Scottish Government cannot simply continue to say that the number of nurses working in the NHS is higher now than it was a couple of years ago. There are more than 1700 nursing posts currently vacant which tells us that health boards are struggling to find the staff they say they need.
"This situation raises concerns about how health boards will be able to staff all the services needed for a proper seven-day NHS service."
A spokesman for BMA Scotland said: "Any plans to increase consultant presence during weekends needs to recognise that, without a significant increase in workforce, there will be a reduction during the weekdays."
The Herald's NHS: Time for Action campaign has highlighted the growing pressures on hospitals and argued for a review of capacity across the health service.
The concerns about weekend staffing came days after NHS Lanarkshire was ordered to make widespread improvements in the wake of a damning inspectors' report. An inquiry into mortality rates at Wishaw, Monklands and Hairmyres hospitals found serious problems with understaffing, quality of care and record-keeping.
In October, Health Secretary Alex Neil said he wanted hospitals to improve weekend cover following evidence that death rates were higher than on weekdays.
A spokeswoman for the Scottish Government said all board were expected to ensure they had appropriate staff at all times, and that resources were being provided to increase staffing levels.
She added that the Government was targeting enhanced weekend and out-of-hours services. "A key part of this issue is how patients flow through hospitals, and we have invested £4 million to test innovative approaches from across the world in that area."