Heroin addicts were recruited for a 14-week open clinical comparison of methadone hydrochloride and methadyl acetate. Patients were randomly assigned to a methadyl acetate clinic in which methadyl acetate was dispensed to patients three times per week or to a methadone clinic in which methadone was dispensed six days per week. No statistically significant differences were observed between groups in retention rates, illicit drug use, employment rates, or arrest rates. The group treated with methadyl acetate had more dropouts in the first seven weeks than the second seven weeks: this pattern was reversed for the methadone-treated group. The differences were significant (P = .01). Spontaneously reported symptoms suggest that induction with methadyl acetate may be a more clinically variable phenomenon than induction with methadone. The reduction of number of clinic visits in the group treated with methadyl acetate was not a source of variance in treatment effectiveness.