A number of cases of Loa-encephalopathy have been reported following ivermectin (Mectizan) treatment for onchocerciasis in patients with high Loa microfilaraemia. A possible explanation for these severe reactions is the formation of micro-emboli in small brain vessels as a result of massive paralysis of Loa microfilariae in the blood. This suggests that encephalopathy might be prevented by giving an initial low dose of ivermectin to induce a more gradual action on the Loa microfilariae. To test this hypothesis, a trial was conducted on 23 adult patients in Cameroon. Patients were divided into two groups. One group received the recommended dose of 150 micrograms/Kg. The other group received a lower dose of 50 micrograms/Kg (one 3 mg tablet of Mectizan). Blood smears were made daily from day 1 to 7 after treatment and then on days 15 and 30. Results showed no difference in the effect of the dosage level on Loa microfilaraemia. This finding suggests that an initial low dose of 3 mg Mectizan will not prevent encephalopathy following treatment for onchocerciasis.