PIP: The urinary excretion of pregnanediol was estimated during the luteal phase of the menstrual cycle, pregnancy, and the puerperium in langur monkeys. Pregnanediol 1st appeared in urine on the day after ovulation and reached peak values on Day 17 of the cycle. Pregnanediol levels rapidly fell on Day 20 to the point that they could not be estimated. Pregnanediol appeared to be the major progesterone metabolite during pregnancy, though 6 other metabolites, including androsterone and dehydroepiandrosterone, were also present. 2 days following parturition, pregnanediol levels were undetectable. It is suggested that this species (Presbytis entellus entellus) could be used as a model for the study of progesterone metabolism in human females.