Methylphenidate-induced hepatic injury was documented by abnormal liver function tests including a markedly elevated serum bilirubin, serum glutamic oxaloacetic transaminase, and serum glutamic pyruvic transaminase. Liver biopsy confirmed portal inflammation and hepatocellular disarray. Enzyme changes were reproducible with rechallenge of the drug (Ritalin). The drug is capable of producing hepatic injury, particularly when given in nonstandard doses intravenously.