The use of enzyme hydrolysis of urinary progesterone metabolites with subsequent determination by radioimmunoassay of the resultant progestin concentrations was evaluated for its ability to assess luteal function in the false killer whale (Pseudorca crassidens). Two female whales were trained for voluntary urine collection. Daily to weekly samples were collected for up to 2 years. Detection of non-specific urinary progestin concentrations was accomplished through enzyme hydrolysis of the urinary progesterone conjugates. Immunoreactive urinary progesterone concentrations (iPo) indexed by creatinine (cr.) were compared to plasma progesterone (Po) concentrations. Comparisons between serial having dilutions of the progesterone standards and concentrated urine samples exhibited parallel displacement curves. The concentration of iPo in the pseudorca ranged from 12. l ng/mg cr. during nadir to 22 l .3 ng/mg cr. during the early gestational period. Animal l had 3 periods of elevated Po and iPo of approximately 378 days, 202 days and 36 days before she became pregnant. The gestation length for animal l was 14 months. Animal 2 had only one period of elevated Po and iPo lasting approximately 24 days before she became pregnant toward the end of the sampling period. The data provide the first information concerning false killer whale endocrinology and they demonstrate that the use of urinary progestin concentrations in conjunction with sporadic serum progesterone values can be used to determine luteal function in false killer whales.