In the course of a parasitological survey conducted by the U. S. Army in the vicinity of Roberts Field, Liberia, larval filariids were found in 6 of 649 (0.9%) [female] Anopheles gambiae dissected. Numerous cases of elephantiasis, notably scrotal enlargements, were observed among the Liberian natives. 14 cases of infection with Wuchereria ban-crofti microfilariae and 2 of Acanthocheilonema Persians were detected in daytime blood examinations of 2134 Liberian natives (0.75%). Four nocturnal surveys of 955 residents of 5 native villages revealed about 8.8% of the population . positive for microfilariae. All cases were W. bancrofti except one infection with A. perstarts. Age group analyses indicated that infection is acquired during the early years of life and continues into adulthood. Most of the cases of microfilare-mia were symptomless. No microfilariae were found in 431 American soldiers who had been stationed in Liberia for at least a year.