The effectiveness of treating human brucellosis caused by Brucella melitensis with a 6-week course of doxcycline plus streptomycin for 2 of those weeks was analyzed by a multicenter prospective study of 139 patients. Subjects with central nervous system involvement, endocarditis, or spondylitis were excluded from the study. All but 5 of the 139 patients completed the full treatment schedule and became afebrile in the first week of therapy. Four patients suffered relapses during the follow-up period. Of the five patients who did not complete the treatment, two left because of adverse secondary effects (1.4%), another two left for noncomplicance with the treatment (1.4%), and the remaining patient was considered a therapeutic failure because his symptoms persisted after the first week of therapy (0.7%). We concluded that the combination of doxycycline and streptomycin is an effective treatment for the types of brucellosis included in our study.