The effect of malnutrition on hepatic drug-metabolising enzymes was investigated in 8 Sudanese children aged between 9 and 12.5 years using as a model the drug antipyrine. Antipyrine half-life and clearance were measured in the malnourished state and after 3 or 4 weeks of good nutrition. Associated with the improvement in nutritional state was a shortening of antipyrine half-life and an increase in its clearance. There was also a rise in serum triiodothyronine. It is concluded that poor nutrition is associated with impairment of drug metabolic capacity and that many factors are responsible.