SUMMARY: Urinary steroids and steroid conjugates were measured in the squirrel monkey (Saimuri sciureus). The principal steroids excreted were cortisol, 11β,17α,20β,21-tetrahydroxy-4pregnen-3-one (20β-dihydrocortisol), 11β,17α,20α,21-tetrahydroxy-4-pregnen-3-one (20α-dihydrocortisol), α- and β-cortol and α- and β-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 3α,17α,21-trihydroxy-5β-pregnane-11,20-dione (tetrahydrocortisone) and 3α,11β,17α,21-tetrahydroxy-5β-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 3β,17α,20ξ,21-tetrahydroxy-5β-pregnan-11-one. Administration of dexamethasone resulted in complete suppression of steroid output, whilst the response to adrenocorticotrophic hormone was inconstant.