Urinary steroids and steroid conjugates were measured in the squirrel monkey (Saimuri sciureus). The principal steroids excreted were cortisol, 11beta,17alpha,20beta,21-tetrahydroxy-4-pregnen-3-one (20beta-dihydrocortisol), alpha- and beta-cortol and alpha- and beta-cortolone. The majority of the steroids were excreted unconjugated and a conspicuous feature of the pattern was the large amount of urinary free cortisol. Unlike man there was an insignificant excretion of 3alpha,17alpha,21-trihydroxy-5beta-pregnane-11,20-dione (tetrahydrocortisone) and 3alpha,11beta,17alpha,21-tetrahydroxy-5beta-pregnan-20-one (tetrahydrocortisol). A steroid not previously identified in urine from any species was one of the major glucuronide conjugates; it was characterized as having the structure 3beta,17alpha,20xi,21-tetrahydroxy-5beta-pregnan-11-one. Administration of dexamethosone resulted in complete suppression of steroid output, whilst the response to adrenocorticotrophic hormone was inconstant.