A public sector watchdog has warned health officials to monitor their use of temporary nurses.
Bank nurses can provide absence cover at short notice
Audit Scotland highlighted the growing use of bank nursing staff by NHS bosses as a way to cope with staff shortages.
Bank nurses are health service employees who can be called on at short notice to cover both planned and unplanned absences.
The report said the trend must be closely monitored to ensure quality of care was maintained.
The use of agency nurses, who are employed by commercial nursing agencies, fell by 17% between 2001/02 and 2005/06, while the use of bank nursing staff increased by 73% over the same period.
The report said: "This trend needs to be monitored to ensure that the quality of care is maintained and appropriate use is made of bank and agency staff."
The increase in use of bank nurses meant about 5.5% of the total nursing spend in 2005/06 went on bank and agency staff, with the bill reaching £96m.
Nurses and midwives make up the largest single staff group within the NHS, with 55,469 full-time equivalent workers.
The Audit Scotland report also highlighted the need for better workforce planning, pointing out that most NHS boards have not met national recommendations on building additional time into staffing requirements to take account of factors such as holidays, sickness and maternity leave.
Robert Black, the Auditor General for Scotland, said: "Nurses are crucial to the delivery of good quality patient care and so it is good news that the health service has responded to the previous ward nursing report and is laying the foundations for better workforce planning in this area.
"I recognise that this is not an easy thing to get right. The NHS now needs to build on progress made and ensure it has the information needed to manage the workforce well.
"The use of bank and agency nurses also needs to be kept under review."