Single venous blood samples were collected from 52 hyaenas and serial samples via indwelling jugular catheters from 8 hyaenas. Social status of the hyaenas was unknown. Radioimmunoassay estimations were specific for testosterone, androstenedione, cortisol and LH. No significant differences could be found between the sexes for concentrations of testosterone (adult males 2.9 +/- 1.3 nmol/l; adult females (non-pregnant) 1.6 +/- 0.3 nmol/l). Androstenedione concentrations in sub-adult males were significantly lower than those in females (2.3 +/- 0.05 and 5.5 +/- 1.2 nmol/l). Testosterone and androstenedione concentrations were significantly higher in parous pregnant than in parous non-pregnant females (4.3 +/- 1.4 and 1.6 +/- 0.3; and 23.7 +/- 11.6 and 6.7 +/- 0.9 nmol/l respectively). Both LHRH and hCG elicited elevated androgen concentrations in females in different reproductive categories. Androgens are produced by the ovary in the absence of follicular or luteal structures, indicating androgen production by the interstitial tissue of the ovarian stroma.