Androgen-resistant female mice (Tfm/Tfm) homozygous for the mutant gene Tfm were bred by making use of males chimaeric for the Tfm gene. All seven Tfm/Tfm females found were fertile, confirming that a normal level of androgen receptor protein is not essential for reproduction in female mice. However, when five of the seven were studied throughout their reproductive life they proved to have impaired reproductive performance and premature cessation of reproduction. No impairment of reproduction was seen in heterozygous Tfm/+ females. The ovarian histology suggested that in Tfm/Tfm the normal ageing processes were accelerated. This work is consistent with the work of others in that androgen is involved in the control of follicular maturation and atresia, and that the effect is mediated by the androgen receptor coded by the Tfm locus.