Response to treatment with organic pentavalent antimonials, the standard first-line treatment for visceral leishmaniasis (VL), has been decreasing since their introduction into India. Combining sodium stibogluconate (SB) with paromomycin (PM) may be an efficient alternative to single-agent therapy. This trial was designed to assess the safety and efficacy of PM 12 or 18 mg/kg daily plus SB 20 mg/kg daily for 21 days compared to SB alone for 30 days. One hundred and fifty patients were randomly assigned in 1996 to 1 of the 3 treatments and followed-up for 180 days. At the end of treatment, 49 of 52 patients receiving PM12 + SB, 46 of 48 receiving PM18 + SB, and 27 of 49 patients receiving SB alone, were cured. During follow-up there was 1 relapse in each of the treatment groups, giving final cure rates of 48 of 52 (92.3%) for PM12 + SB, 45 of 48 (93.8%) for PM18 + SB, and 26 of 49 (53.1%) for SB. PM plus SB for 21 days at either 12 or 18 mg/kg daily was significantly more effective than SB alone for 30 days (chi 2 P < 0.001). One patient (SB alone) had experienced a serious adverse event: cardiotoxicity at day 8 (myocarditis and ECG changes) which caused withdrawal from the study. Only 19 of 100 patients enrolled in the PM treatment arms had a complete audiogram series conducted thus making it difficult to assess oto-toxicity. PM 12 or 18 mg/kg daily plus a standard dose of SB for 21 days was statistically more effective than SB in producing a final cure for patients with VL in Bihar, India.