Cats excreted 19.2 ± 1.5% of free morphine and 48.4 ± 2.4% of conjugated morphine in urine during the first 48 hr. after subcutaneous injection of morphine. Fecal excretion during 2 days following drug administration ranged from 2.0 to 20% of the injected drug. The major morphine conjugate was isolated and characterized as morphine-3-ethereal sulfate by UV and IR spectra, morphine content, and elemental analysis. In addition to morphine-3-ethereal sulfate, morphine-3-glucuronide and normorphine were also identified as minor metabolites.