Seventeen male and 39 female Liberian patients, one third of them children, were diagnosed as having hyperreactive onchodermatitis (sowda). They presented with itching (98%), asymmetric (98%), chronic onchodermatitis (median 5 years), and swelling of femoral lymph nodes (89%). The geometric means of the microfilaria (mf) densities were 1.0 mf/mg in children and 0.7 mf/mg in adults. These patients not only suffered from their skin lesions, and severe itching resulting in disturbance of sleep but also from social stigmata. They urgently needed treatment. Ivermectin was administered as a single oral dose of 150 micrograms/kg body weight. The following adverse effects were observed in 30 patients within the first 72 hours after ivermectin treatment: increase of pruritus (93%), aggravation of dermatitis (73%), fever (25%), headache (20%), myalgia (20%), painful swelling of lymph nodes (13%) and severe swelling of arm or leg (10%). Symptomatic therapy was sufficient. No dangerous or life-threatening side effects were observed. At follow-up examinations 1-2 months after ivermectin treatment, the prevalence of mf carriers had decreased from 100% to 19%. Seventeen out of 18 patients felt their dermatitis had improved. Evaluation of the dermatitis by a physician using a score from 0 (no dermatitis) to 9 (severe dermatitis) revealed a reduction of the score from 4.3 before treatment to 0.7 (84%) after ivermectin. In contrary, at the follow-up examination of 16 patients 6-12 months after ivermectin some recrudescences were observed. In this group the prevalence of mf carriers was 47%, 13 out of the 16 patients felt their skin lesions had improved and the score had decreased from 2.2 to 0.5 (77%). Consequently, it is recommended to administer ivermectin to patients with hyperreactive onchodermatitis every 3-4 months.