Urinary androgens were measured using a single antibody testosterone RIA. Testosterone standards (7.8-1000 pg per tube; ICN Biomedicals, Costa Mesa, CA) and 0.01 ml of unprocessed panda urine were combined, in duplicate, with testosterone antiserum (0.1 ml, 1:16 000; ICN Biomedicals) and tritiated testosterone (10 000 counts per minute per 0.1 ml diluted in PBS; New England Nuclear). Assays were incubated overnight (4°C), and bound and free ligands were separated by adding a charcoal dextran solution (0.25 ml) for 30 minutes (4°C). Samples were centrifuged (1500 g, 15 minutes), and the supernatant was counted for radioactivity. Intra- and interassay variation was <10% and 20%, respectively (n = 30).

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