Post-mating non-infectious hydrometra and hydrovagina of unknown aetiology, leading to a scrotum-like swelling of the perineum, was observed during an experiment on BALB/c: Bom mice. There was a closure of the vulva with accumulation of secretions of uterine glands under high pressure in both uterus and vagina. The mice were otherwise clinically healthy, gained body weight normally, but were incapable of breeding. The morbidity was approximately 1% and the disease could not be transmitted to other females.