The population of eleven villages in the savanna area in Upper Lofa in the hinterland of Liberia was investigated in 1973 and 1976/77 for infections with microfilariae of Wucheria bancrofti. From a total of 1255 persons examined in 1973 16,3% were microfilaria carriers and in 1976/77 17,9% out of 1356 inhabitants were microfilaria positive. To obtain informations on the change of microfilaraemia in individuals, emphasis was laid in 1976/77 on the identification of those persons, who had been examined already in 1973. From 477 persons examined in both surveys 78 proved to be infected with microfilariae and 348 were microfilaria negative in both examinations. 35 inhabitants were microfilaria positive only in 1976/77 and 18 persons showed microfilariae in the blood samples only in 1973. The median density of microfilariae of the microfilaria carriers examined in 1973 and 1976/77 increased little but statistically significantly within a period of about three years.