Adult undernourished tuberculous patients receiving isoniazid, rifampicin and ethambutol were evaluated clinically and biochemically for hepatic dysfunction. The nutritional status was assessed by body-mass index, serum albumin and haemoglobin. While only 11% of the patients developed jaundice, the majority of the patients had a significant elevation of the serum hepatic enzymes suggesting subclinical hepatotoxicity. A significant downward trend during the 3-6 months period was seen in patients with multiple estimations of SGOT and SGPT indicating a self-limiting toxic process. However, the continued elevation of GGT suggests enzyme induction by rifampicin. Undernutrition contributes to drug toxicity by various mechanisms. Therefore, it is important to evaluate the nutritional status of the tuberculous patients receiving drugs, which are potentially hepatotoxic.