Poor management is to blame for the high cost of locum medical cover, a report by the Accounts Commission for Scotland says.
It says spending by Scottish trusts has almost doubled to pounds 17m over four years - but that they could save pounds 1m a year by more effective management of medical cover.
The report says managers make unnecessary use of locums, which in turn encourages moonlighting among junior doctors, who then work excessive hours and put patients at risk.
It says better management of existing staff, a cut in the use of agencies and, where agencies are used, encouraging all trusts to engage in collaborative tendering could save pounds 1m a year.
And it argues that pressure to fill vacancies quickly means that vetting and induction procedures are not as thorough as they should be.
The report says a personnel manager at one trust received a phone call from a nursing officer complaining that the locum on duty was constantly falling asleep.
He admitted that he had already worked 100 hours that week at his own trust - a fact not mentioned on appointment. He was sent home without pay. No action was taken to report the incident to the doctor's home trust.
The Scottish Office says it issued guidance in January to address areas of concern raised in the report. 'This report has largely been overtaken by events,' said a spokesperson.
Lorna Naismith, human resources director at Glasgow Royal Infirmary, did not consider locum cover a problem. 'Our use of locums is low. The trust has an arrangement with one agency which we very strictly control,' she said.
A spokesperson for Edinburgh Royal Infirmary said that since the Scottish Office guidance was issued, locums were no longer used to cover doctors' holiday leave. A spokesperson for the Audit Commission said it was considering undertaking a similar survey to examine the use of locum cover by trusts in England and Wales next year.
Doing the Rounds. Accounts Commission for Scotland, 18 George Street, Edinburgh EH2 2QU. Also at www.Scot-ac.gov.uk Free.