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Filarial loiasis differs from other filariases in that most infected subjects are amicrofilaremic. This difference raises the notion of occult infection. The aim of this study was to evaluate the relationship between the intensity of transmission and incidence of infection. For this purpose we determined the incidence of loiasis both microscopically and by PCR in 201 subjects from three villages in the province of Haut Ogooue in Gabon. Intensity of transmission, expressed in ATP (annual transmission potential) in these villages was estimated to be 250 infecting larvae per individual per year (L3/man/yr) in Moyabi, 180 L3/man/yr in N'dokaye, and 43,000 L3/man/yr in Okoumbi. Although there was no significant difference between the three villages with regard to the incidence of microfilaremia (21 p. 100 and 22 p. 100), the incidence of occult infection, i.e., positive PCR in amicrofilaremic subjects, was 45 p. 100 in Moyabi, 79 p. 100 in N'dokaye and 80 p. 100 in Okoumbi. The overall incidence of loiasis was 57 p. 100 in Moyabi and 85 p. 100 in both N'dokaye and Okoumbi. These findings demonstrate that the incidence of loiasis is correlated with the intensity of transmission (p < 0.001), especially in children. Taking this information into account will improve control of Loa loa in endemic areas.