A prospective study was performed in clinically malnourished patients in which liver function was tested during a 4-week period of total parenteral nutrition (TPN). The purpose was to determine if concomitant intravenous lipid administration would reduce liver function abnormalities noted to occur frequently in patients receiving TPN. Twenty-five patients were randomly assigned to receive either daily infusions of 200 cc of a 20% lipid emulsion with TPN or TPN without lipid for the first week. In the subsequent 3 weeks all patients received daily intravenous lipid. The early lipid treatment group received 0.7 g lipid/kg BW/day and approximately 280 mg of choline/day from the lecithin emulsifier throughout the entire study period. Liver function tests were performed twice in the first week, then weekly thereafter. There were significant (p less than 0.05) elevations in liver function tests in the early lipid treatment group (for aspartate aminotransferase in weeks 1, 2, and 3, and lactic acid dehydrogenase in weeks 2 and 3). Alkaline phosphatase activity was elevated at weeks 2, 3, and 4 for the lipid-treatment group and at week 1 for the lipid-restricted group. The two groups had a similar elevation in gamma-glutamyltransferase activity. Analysis of covariance demonstrated that the overall duration of TPN, and not the presence or absence of intravenous lipid, was significantly related to the elevations in both alkaline phosphatase and gamma-glutamyltransferase (GGT) levels. In contrast, the early intravenous administration of lipid was significantly related to the increase in aspartate aminotransferase levels. The peak increase in AST was noted at day 7 in the lipid-administration group.(ABSTRACT TRUNCATED AT 250 WORDS)