The plasma levels and urinary excretion of chloramphenicol was studied in ten malnourished children and four normal children after oral administration of a single dose of 25 mg/kg body weight. Plasma peak levels were achieved 2-4 hours later and were 1.5 or 2 times higher in malnourished children compared to the normal. They also took much longer to clear the drug from the plasma, 30 hours or more in malnourished children compared with 12 hours in the normal. These observations point to a slower rate of biotransformation in the liver. The excretion pattern of the drug and its metabolite lends support to this hypothesis. 75-85% of the drug excreted was in the form of conjugated fraction in the normal while only 35-55% was conjugated in malnourished children. In two children the liver biopsy tissue was subjected to assay of bilirubin-UDP transferase and low levels were detected. This observation also points to an alteration in the rate of biosynthesis of chloramphenicol.