The pharmacokinetic profile of (-)-2-hydroxy-N-cyclopropylmethylmorphinan (HCMM), a narcotic antagonist and analgesic, has been evaluated in man following administration of 25 to 50 mg of the drug orally and 10 to 15 mg intramuscularly. A specific radioimmunoassay procedure was developed for the determination of HCMM in plasma and urine. The drug had a mean "apparent" elimination half-life in plasma of about 11 hr following both routes of administration. A mean of 47% of the oral dose was excreted in the urine as unconjugated and conjugated HCMM and only 5% of the dose was excreted as intact HCMM. In one subject studied, the plasma levels of conjugated HCMM were as much as 5-fold higher than the levels of unconjugated drug. Although there was considerable intersubject variability following both routes of administration, the overall pharmacokinetic parameters suggest that oral and intramuscular doses are bioequivalent.