The clinical presentation of kala-azar in 43 children and 45 adults was compared. In both groups fever, left upper quadrant abdominal pain and swelling, and weight loss were equally the most common presenting symptoms. Lymphadenopathy was observed in 86 per cent of children and 76 per cent of adults. Splenomegaly was absent in 2 per cent of children and 7 per cent of adults. No significant difference was found in frequency distribution of symptoms and signs between children and adults. Haematological indices were compared in both children and adults with kala-azar and their control groups. In both children and adults with kala-azar, haemoglobin concentration, total white cell count, and platelet count were significantly lower before than after treatment. Only haemoglobin concentration was lower in children with kala-azar as compared with adults with the disease. Children in the control group had lower haemoglobin and higher total white cell count than adult controls. Response to therapy was evaluated in 693 patients. Two-hundred-and-fifty children and 373 adults were treated with sodium stibogluconate 10 mg/kg for 30 days; in both groups 12 per cent deaths and 4 per cent relapses occurred. Thirty children and 40 adults were treated with sodium stibogluconate 2 x 10 mg/kg for 15 days. In children, 3 per cent deaths and 7 per cent relapses were noted; in adults there were 8 per cent deaths and 5 per cent relapses. No significant difference in death rate or relapse rate was found between children and adults in both regimens. Both regimens performed equally well in children and adults with regard to death rate and relapse rate.