Summary There was very little difference between the number of patients demonstrated to have microfilariae of Wuchereria bancrofti or in the number of microfilaria per smear as measured by scarification or by ordinary thick blood smears. Hourly thick blood smears using 20 cmm. of blood made on 12 subjects demonstrated that the most satisfactory time for making night blood examinations was between 9 and 11 pm. The concentration of microfilariae on night smears was about six times that on day smears in the periodicity examination, but about 15 times the day rate in actual practice. Forty-two or 3.0% of 1395 day smears and 53 or 10.2% of 520 night smears contained microfilariae of Wuchereria bancrofti. No Loa loa was observed but six had Acanthocheilonema perstans. Parasitemia due to W. bancrofti was much commoner along the coast than in the interior locations. This may be dependent upon the presence of the brackish-water-breeding Anopheles melas along the coast which has been demonstrated to have a very much higher filarial infection rate than other potential vectors.