Buprenorphine was significantly more effective than morphine in reducing the duration of treatment, with a median between-group difference of 13 days in the intention-to-treat analysis. This difference translated into a similarly significant reduction in the length of hospital stay. Results were similar in the per-protocol analysis and the as-treated analysis. We found no significant differences between groups in the need for adjunctive phenobarbital treatment, although few infants in either group received this treatment. These findings suggest that the pharmacodynamic effects of buprenorphine and morphine may not differ substantially at the predefined maximal doses.