The effect of prescribing guidelines on the use of neuromuscular blocking agents (NMBs) was studied. Voluntary guidelines on the appropriate prescribing of formulary NMBs in the operating rooms at a university hospital were approved in January 1993. Patients who underwent inpatient surgery with neuromuscular blockade during a preguideline period (March 1, 1992, through May 31, 1992) or a postguideline period (March 1, 1993, through May 31, 1993) were randomly selected (n = 200 per group) and compared to determine the relative appropriateness, effectiveness, safety, and cost of NMB use. The preguideline and post-guideline groups were demographically similar. There were significantly more instances of appropriate NMB use after than before the guidelines were established. Neuromuscular blockade was maintained inall patients. The overall rates of NMB-associated adverse events were 5.5% and 7.5% for the preguideline and postguideline groups, respectively. The acquisition cost of NMBs and drugs used to treat NMB-associated adverse events for the preguideline patients was $4261, versus $2978 for the postguideline patients. Extrapolated to the estimated 10,000 operations per year requiring neuromuscular blockade at the institution, the total cost was $213,000 before guideline introduction and $149,000 afterward, for a guideline-associated cost reduction of $64,000. Prescribing guidelines reduced expenditures for NMBs without affecting clinical outcomes.