A sero epidemiological study involving 5009 individuals resident in the two largest cities (Ibadan and Benin) in the Western Region of Nigeria has been carried out, using the LGVCFT to determine the presence of LGV antibodies. These individuals come from various population groups and social classes (i.e. blood donors, antenatal clinic patients, general out-patients, venereal diseases clinic patients and prostitutes). Among the 3638 subjects tested in Ibadan, the seroreactivity rates ranged from 5.3% to 11.5%, while of the 1371 in Benin, the seroreactivity ranged from 7.3% to 18.3%. The seroreactivity rates confirm previous suspicion that there is a considerable reservoir of infection among the female population both in normal women and in prostitutes. While the value of LGVCFT as an epidemiological tool in the estimation of latent or active infection in a community has been substantiated, a puzzling variation in the endemicity of the LGV agent, even within the same region, has been observed. It is suggested that routine testing of blood donors and antenatal women with LGVCFT such as done with serological tests for syphilis should be carried out in tropical countries where LGV is endemic.