Abstract 1. 1. Conjugative metabolism and biliary excretion of phenolphthalein (PP) were studied in steelhead trout ( Salmo gair dneri) acclimated to 10, 14 or 18°C. 2. 2. Significant seasonal effects were found on liver weight to body weight ratio and conjugative metabolism but not biliary excretion of free plus conjugate of PP. Temperature did not significantly interact with these relationships. 3. 3. PP was excreted in bile as parent compound and the glucuronide conjugate at all temperatures. 4. 4. Saturation of the excretory process was apparent at a dose of approximately 10 μmol/kg (i.p.) at 10 and 14, but not 18°C.