Summary. Studies of 3 genetically female, intersex pigs revealed that only one showed oestrous cycles and lordosis, the other 2 exhibited various components of male sexual behaviour. Each uterus was a patent bicornuate structure, but 5 of the oviducts were incompletely formed. Two of the animals had bilateral ovotestes, whilst the third had a functional ovary on the right and an ovotestis on the left. The small ovarian portion of each ovotestis contained Graafian follicles which did not respond to a systemic injection of PMSG. The major portion of each ovotestis consisted of extensive interstitial tissue and seminiferous tubules devoid of germ cells. A structure closely resembling an epididymis adjoined the ovotestes. Concentrations of oestradiol and progesterone in plasma corresponded with those expected in the follicular phase of an oestrous cycle, but concentrations of testosterone represented approximately one-tenth of the values found in mature boars.