Sexuality, aggression, and mood were investigated in 14 presurgical male-to-female transsexuals, undergoing antiandrogenic treatment with anandron, a pure antiandrogen. Subjects were given a test battery the morning prior to treatment onset and after 8 weeks of treatment. In addition they were requested to complete daily forms concerned with sexual behavior and mood. Morning erections and the frequency of thoughts and fantasies about sex decreased after anandron intake. Aggressive feelings were uncorrelated with testosterone level. Moods such as level of energy, feelings of relaxation, fatigue, and feelings of tension and anxiety appeared to fluctuate more as a consequence of anandron intake than did moods such as cheerful, sociable and friendly, gloomy and unhappy, irritated and changeable. The latter remained at a constant level.