To study the distribution of selenium metabolites in whale urine, an analytical methodology for separation and determination has been developed. 2. From whale urine, five selenium components, including trimethylselenonium ion were separated and determined by a combination of ion exchange chromatography and fluorometry. 3. The mean urinary selenium level of five minke whales was 1500 ng/ml, with a standard deviation of 400 ng/ml, i.e., about 30 times as high as that for humans.