Female golden hamsters received one of the following treatments on the day following birth: (i) 300 mug testosterone propionate in arachis oil, (ii) 300 mug testosterone in oil, (iii) 300 mug dihydrotestosterone in oil, or (iv) oil alone. As adults all animals, underwent three tests for behaviour. First, while intact, females were observed in aggressive interactions with males. Secondly, after ovariectomy, females were primed with oestrogen + progesterone and tested for receptivity with a stud male. Thirdly, all ovariectomized females were primed with testosterone propionate and tested for male patterns of behaviour with a receptive female. Compared with the effects of oil administration (control), testosterone propionate administration resulted in increased aggressiveness and the capacity to show male patterns of sexual behaviour, together with a decreased capacity to show female patterns of sexual behaviour. Testosterone increased aggression and male sexual behaviour, but had no effects on receptivity, while dihydrotestosterone decreased some components of receptivity but had no effects on aggressiveness or the capacity to show male mating behaviour.