Levamisole is an immunopotenciator drug which is used as an antihelmintic drug as well as very effective remedy on cellular immunity compared with humoral immunity. A total 71 patients (37 men, 34 women) who referred to our department between March 1997 and December 2001, with a history of the disease for about 1 year, were diagnosed as having chronic brucellosis through those tests brucella serum agglutination test (SAT), SAT with Coombs and SAT with 2-mercaptoethanol. The patients were randomly divided into levamisole group (36 patients) and control group (35 patients). All patients were given rifampicin 600 mg/day + doxycycline 200 mg/day for 6 weeks as a standard classical combined therapy for brucellosis. In the levamisole group, oral levamisole 80 mg every other day for 6 weeks was added to the treatment. There was a statistically significant difference between two groups, in complaints of arthralgia, fatigue and sweats before and 6 months after treatment, as well as in erythrocyte sedimentation rate and C-reactive protein elevations and lymphomonocytosis finding. While it was provided both clinical and serological improvement in all patients in the levamisole group; 11 patients in the control group did not improve both clinically and in view of specific and nonspecific laboratory findings and a recurrence occurred in one case, in this group. In conclusion, levamisole added to classical antibiotic therapy in treatment of chronic brucellosis was found quite efficient in all patients in providing adequate clinical and laboratory response in comparison to classical antibiotic therapy alone.