We conducted a prospective, noncomparative, multicenter study to assess the safety and efficacy of doxycycline and netilmicin in the treatment of human brucellosis. The study included 64 patients who had acute brucellosis without endocarditis or neurobrucellosis. The treatment schedule consisted of the administration of 100 mg of doxycycline (or 5 mg/[kg.d] if body weight < or = 40 kg) twice a day orally for 45 days, plus 300 mg of netilmicin (6 mg/[kg.d] if body weight < or = 50 kg) intramuscularly once daily for 7 days. Therapeutic failure was noted in 5 patients (7.7%; 95% confidence interval [CI], 2.5%-17.1%), of whom 2 had spondylitis, 1 had sacroiliitis, and 1 had a splenic abscess that required splenectomy. Relapse was noted in eight patients (12.5%; 95% CI, 5.6%-23.2%). When relapse was considered in combination with initial lack of efficacy, 13 patients (21.9%; 95% CI, 12.3%-33.9%) failed to respond to therapy. Fifteen patients (23%; 95% CI, 13.5%-35.2%) had adverse effects, and one patient (1.5%) had a treatment-limiting adverse effect. Combination therapy with netilmicin/doxycycline may be effective in treating acute brucellosis. However, prospective controlled trials must confirm these results.