A number of studies have established the clinical efficacy of naltrexone in the treatment of opiate addiction. However, questions have been raised regarding its hepatotoxic potential and warnings have been given prominence in the package insert regarding its use for those with even less severe liver disease. The current study monitored 53 male patients receiving naltrexone 350 mg weekly for 12 weeks. The lactic acid dehydrogenase (LDH) and serum glutamic oxalacetic transaminase (SGOT) levels were determined at pretreatment and at monthly intervals thereafter for three months. LDH and SGOT were found to drop significantly from baseline over this three-month period. This decrease appeared most notable for those with pretreatment hepatic enzyme levels exceeding the normal range. Moreover, changes in hepatic enzyme levels were not consistently correlated with the patients use of illicit drugs such as opioids, benzodiazepines, cocaine, barbiturates, and amphetamines. Based on these data, we have concluded that contrary to cautions implied in the naltrexone package insert, the benefit of admitting patients with the sole problem of elevated hepatic enzymes generally exceeds the risk.