Examining gonadal function in the small excitable cotton-top tamarin monkey (Saguinus oedipus) requires noninvasive sampling techniques. Two studies were performed to identify the quantifiable urinary metabolites of testosterone in cotton-top tamarins and which of the measurable metabolites would best reflect a gonadal source of testosterone secretion. In the first study, we injected unlabeled testosterone i.m. in males at either 500-ng or 1-microg levels. Urine samples were analyzed for androgens and estrogens. Testosterone and dihydrotestosterone (DHT) increased significantly following the injections in test males but not in control males. No significant increases in androstenedione occurred. Mean levels of estradiol and estrone did not consistently increase during the 5 days following injection. In the second study, a gonadotropin-releasing hormone antagonist, Antide, was used to block LH stimulation of gonadal steroidogenesis. Males given Antide at either a 6 mg/kg dose or an 18 mg/kg dose showed significantly lower levels of urinary LH than controls. At the higher Antide dose, testosterone levels were significantly reduced during weeks 1 and 2 posttreatment, whereas DHT levels significantly declined during the 2nd week posttreatment. Estradiol levels were highly variable prior to treatment but decreased significantly following treatment, whereas estrone levels remained variable throughout. These results indicate that measurement of urinary testosterone and possibly DHT reflect gonadal function in male cotton-top tamarins. Other sources of urinary estrogens may occur for the male cotton-top tamarin, but these data suggest that a substantial part of urinary estradiol is from gonadal sources, whereas urinary estrone appears to be mainly from extragonadal sources.