Serum levels of carbohydrate-deficient transferrin (CDT) were determined in a racially mixed population of 107 alcoholics, 18 healthy, nonalcoholic control subjects, 62 abstinent alcoholics, and in 64 Caucasian patients with various nonalcoholic liver diseases. The upper limit of normal CDT levels was 80 mg/liter (2 SD above the mean). CDT values exceeding this level were found in more than 80% of Black, Puerto Rican, and Caucasian alcoholics who had consumed greater than or equal to 50 g of alcohol/day for 1 month or longer prior to testing. Puerto Rican alcoholics had higher CDT values than the Black and Caucasian ethnic groups; however, these differences were significant only when compared to the Black population. Of 64 patients with nonalcoholic liver diseases, one individual with chronic active hepatitis (CAH) with an alcohol consumption of 20 g/day, and 10 of 26 subjects with primary biliary cirrhoses (PBC), who claimed to consume either no or only occasional moderate amounts of alcohol, had CDT levels ranging from 81 to 144 mg/liter. Seven of these individuals were in advanced stages of PBC. Total transferrin levels were variable and not significantly different in all subject groups studied. CDT/total transferrin ratios were increased in most patients with abnormal amounts of CDT, and there was a significant correlation between these ratios and CDT levels in all study groups. Serum enzyme parameters as well as red blood cell mean corpuscular volumes did not correlate with CDT values.(ABSTRACT TRUNCATED AT 250 WORDS)