Social interaction (SI) between two unfamiliar male rats in a dimly lit, familiar environment has been investigated as a model of anxiety, where novelty of the partner remains as the principal anxiogenic stimulus. A range of centrally acting drugs have been tested in this situation. Chlordiazepoxide, nitrazepam, flunitrazepam, and flurazepam all increase SI, as does buspirone, CL 218872, suriclone, sodium valproate, and nicotinamide in the model described. Anxiogenic agents FG 7142 and yohimbine reduced SI without significant modification of motor activities. However, the stimulant amphetamine increased all behaviours in this condition. Amphetamine also increased all behaviours when rats were tested with their cagemates, when the desire for SI is largely satiated. CL 218872 also increased SI in this second situation, and it is suggested that this agent may have a non-specific component in its action in this test. Additionally, caffeine, theophylline, and piracetam may also have non-specific behavioural actions in this model.