Parasitic infections have been reported to be relatively common among the Southeast Asian labourers in Taiwan. This study, conducted in 1992–6, was designed to determine the temporal changes of the prevalence. Faecal specimens were examined by the formalin-ethyl acetate sedimentation technique and blood samples screened using the quantitative buffy coat technique and confirmed by Giemsa stained blood smear. The overall prevalence of intestinal parasitic infections was 10·3%. The annual prevalence decreased from 33·3% in 1992–3 to 4·6% in 1995–6. The Thai (12·0%) and Indonesian (11·1%) had a higher prevalence than the Malaysian (6·7%) and Filipinos (5·9%). Opisthorchis viverrini was the most important parasite in the Thai and Trichuris trichiura in the remaining groups. Moreover, no blood parasites were found in the labourers. The dramatic temporal decline in the intestinal parasitic infections suggests that limiting the entry of infected persons, periodic follow-ups, and immediate treatment of sporadic cases are necessary in preventing transmission of non-indigenous parasites through large population change.