Oestradiol-17beta and progesterone were assayed in the plasma of 32 nymphomaniac cows. In 21 cases oestradiol-17beta concentrations were higher than those recorded during the preovulatory surge of normal cyclic cows. However, for a further 5 nymphomaniac cows oestradiol-17beta concentrations were within the range of those recorded in normal cows during the luteal phase. In 11 cases progesterone concentrations were higher than 1.5 ng/ml, but in only 5 of them could this have been due to a corpus luteum. The presence of progesterone, whether or not associated with a corpus luteum, did not determine the level of oestradiol-17beta. Therefore, nymphomania seems to be less a disease, per se, than a nonspecific symptom of ovarian perturbation.