Three surveys (1997, 1999, and 2001) of outpatient substance abuse treatment centers in Connecticut, Massachusetts, Rhode Island, Maine, Vermont, and New Hampshire examined organizational characteristics that influenced the adoption of naltrexone. Structural equation modeling with manifest variables assessed predictors related to the use of naltrexone. Use of naltrexone increased over time from 14% in 1997 to 25% in 2001. In 1997, programs funded by managed care were more likely, and clinics that provided only substance abuse services were less likely to use psychiatric medication and naltrexone. In subsequent years, counselor education level and organization size also influenced use of naltrexone.