Golden apple snails, Pomacea canaliculata, were collected once a month during a year to search for their natural parasites. The collections were made at two localities having different ecological environments. Of 576 collected snails from a canal, 176 individuals (30.6%) were infected by three groups of metacercariae. These parasites were amphistome, distome and echinostome metacercariae, which had prevalences of 23.5, 19.5 and 0.5%, respectively. The incidence of infection was highest (68.4% in October) when the snail population was composed of the old, juvenile and young Pomacea. Amphistome metacercariae were found most frequently and echinostome metacercariae the least frequently; both parasites were localized in the foot muscle of the snails and had a Shannon index of zero. The range of amphistomes was 1 to 115 with the mean +/- SD of 1 +/- 2 and 95% CL of 1, 2. Distome metacercariae were found primarily in the heart (range: 1-13), and also in the foot muscle (range: 1-5) and kidney (range: 1-14), with a Shannon index of 0.4. The means +/- SD (with 95% CL) were 3 +/- 4 (95% CL = 1, 5), 3 +/- 4 (95% CL = 2, 4) and 2 +/- 1 (95% CL = 1, 2) for the foot muscle, heart and kidney, respectively. The snails from a pond, another locality, had a low proportion of infected individuals. Of 605 snails, only 24 individuals (4.0%) were infected, with the prevalence of amphistomes, distomes and echinostomes being 0.8, 1.8 and 2.1%, respectively. The incidence of infection for each month was zero or less than 10%, except in May when it was 30.2%.