Antibodies to the Pfs2400 gametocyte antigen have been shown to inhibit the development of Plasmodium falciparum in anophelines and therefore this antigen is a candidate for a transmission-blocking vaccine. To test seasonal variation of these antibodies under field conditions, sera from 72 individuals were collected twice, first during the long-rains season with low malaria transmission and then, 6 months later, during the short-rains season, when transmission is high. This study was conducted in several localities in the State of Amapá, Brazil. All but three individuals had a positive indirect fluorescent antibody test (IFAT) with asexual forms of P. falciparum. Most of them did not report malaria attacks during the period between the first and second sampling. Their sera were tested by IFAT with P. falciparum gametocytes. The overall positivity of this test did not vary between seasons, and was 47.2 (34/72) and 48.6% (35/72), respectively. The sera were also tested by ELISA with the Pfs2400 repeat peptide. The positivity rate dropped from 29.2 (21/72) to 15.3% (11/72) and the mean absorbancies from 0.623 to 0.354, when we compared the results of the long-rains and short-rains seasons. Fifteen out of the 21 ELISA positive sera turned negative, with no change of geometric mean of titres (GMT) of asexual IFAT, while five negatives became ELISA positive on second sampling, with increase of GMT. Soon after the second sampling a malaria outbreak was reported in one of the localities. These results point toward a relatively short persistence of anti-Pfs2400 repeat peptide antibodies, under natural field conditions. A gametocyte antigen booster before a high transmission period might contribute towards lowering malaria incidence by eliciting a partially effective antibody response.