The value of programmes to control pulmonary tuberculosis in developing countries remains the subject of debate. We have examined the cost-effectiveness of chemotherapy programmes for the control of pulmonary sputum-smear-positive tuberculosis in Malawi, Mozambique, and Tanzania. Effective cure rates of 86-90% were achieved with short-course chemotherapy and of 60-66% with standard chemotherapy. The average incremental costs per year of life saved were US $1.7-2.1 for short-course chemotherapy with hospital admission, $2.4-3.4 for standard chemotherapy with hospital admission, $0.9-1.1 for ambulatory short-course chemotherapy, and $0.9-1.3 for ambulatory standard chemotherapy. Chemotherapy for smear-positive tuberculosis is thus cheaper than other cost-effective health interventions such as immunisation against measles and oral rehydration therapy. Because the greatest benefit of chemotherapy is reduced transmission of the bacillus, treating HIV-seropositive, tuberculosis smear-positive patients would be only slightly less cost-effective than treating HIV-seronegative, tuberculosis-smear-positive patients.