Sixty-one patients received nitrazepam 5 mg by mouth on the night before operation, followed by 2.5 mg given on the morning of operation and were compared with 60 patients who received no premedication. All were undergoing either therapeutic abortion, by dilatation and curettage, or explorative curettage. The plasma concentrations of nitrazepam were determined by gas chromat-ography and compared with the clinical effects of the drug. The premedicated patients slept better on the night before operation, and were more sedated and less apprehensive. Headache was more frequent following nitrazepam. There was no significant difference between the groups in respect of dizziness and nausea. The unpremedicated patients had a faster average heart rate. There was no obvious relationship between the plasma concentration of nitrazepam and the quality of sleep, degree of sedation, apprehension, excitement or headache.