The effects of protein-calorie malnutrition on bile salt metabolism and liver function were studied. Malnutrition was induced in rabbits by combining litters at 7 days of age (13-16 animals) and results compared to control litters (six-eight animals). At age 29-30 days biliary output from the common bile duct was measured directly for three 1-h periods: under basal conditions, and in response to intravenous infusion of exogenous glycodeoxycholic acid at 0.75 and 1.5 mumol/min/kg, respectively. The bile salt pool size was measured by isotope dilution. Final mean body weight and liver weight were significantly decreased in malnourished animals compared to controls. Liver weight/body weight was also less in the malnourished group. Total liver DNA and protein content, as well as the protein to DNA ratio, were less in the malnourished animals compared to controls. Bile flow and bile salt secretion were reduced in the malnourished group when calculated per kg body weight or per mg liver DNA. Bile salt-dependent flow did not differ significantly, but bile salt-independent flow was significantly less in malnourished animals. Bile salt pool size was decreased in the malnourished group. These findings indicate that malnutrition has a greater impact on liver weight than on total body weight in the preweaning period. In addition, malnutrition reduces bile flow, bile salt secretion, and bile salt pool size which, along with the decrease in bile salt-independent flow, may reflect either an impairment of hepatic uptake function or a delay in postnatal development.