FREE cortisol, luteinizing hormone (LH), total testosterone and monoamines were measured in two successive nocturnal urine collections in 50 healthy men to assess the influence of anticipatory stress. The first collection (N-2) was two nights before and the second (N-1) was just on the night before a one-day experimental stressor consisting of participation in a one-day clinical research protocol. The mean cortisol level increased from 23.4 (N-2) to 66.6 μg (N-1), while mean LH level decreased from 2.68 (N-2) to 1.71 IU (N-l) and the mean testosterone level fell from 1.31 (N-2) to 0.70 μg (N-1). There were no changes in monoamines. Inhibition of sex hormones is a relatively neglected area of stress research.