An unresolved controversy is whether exposure to organic solvents in the workplace causes hepatotoxicity. From a medical surveillance study of 289 printing factory employees who were exposed primarily to toluene, we identified eight workers who had persistently abnormal serum transaminase and/or alkaline phosphatase values. The eight men were generally healthy and gave no history of taking medications or of drinking ethanol to excess. None was obese or diabetic. Six patients had hepatomegaly based on physical examination. All eight had mild elevations (less than 2 to 3 times the upper value of normal) of serum transaminases [alanine (ALT) and aspartate aminotransferase (AST)]. However, there was a marked increase in the ratio of ALT/AST (mean = 1.61). In each case, liver biopsy revealed mild, pericentral fatty change. Our results, consistent with those previously published by some others, suggest that pericentral fatty liver with mild "reactive hepatitis" is the most likely diagnosis in workers exposed to solvents for whom common causes of mild liver test abnormalities have been excluded. An increased ALT/AST ratio may represent a convenient, previously unrecognized indicator of this condition.