Twenty-one male amateur athletes attending a Welsh needle-exchange clinic, were asked to complete the Buss-Durke Inventory on feelings of hostility/aggression, and a feeling state questionnaire. All were weight training in local gyms in order to increase their body mass. They were also using high doses of anabolic steroids during 6-14 week cycles, while between these cycles they were steroid free. Subjects reported significantly higher feelings of aggression, aggression towards objects, verbal aggression, and aggression during training (but not physical aggression towards people), during the on-steroid periods. Other changes on-drug, included significantly higher feelings of alertness, irritability, anxiety, suspiciousness, and negativism. While increased aggressiveness has been noted in many previous studies, the present findings demonstrate that anabolic steroids can affect a wide range of psychological mood states.