A survey of intestinal parasitism was conducted at Yaviza, a town in eastern Panama's Province of Darien. Single stool specimens from 202 persons, representing 11 percent of the town's total population, were examined. In all, 181 (90 per cent) of the specimens examined were found positive for one or more potentially pathogenic parasites. The most common parasite found was Trichuris trichiura, which was observed in 80 per cent of the samples. Others were Ascaris lumbricoides, in 62 per cent of the samples; hookworm, in 41 per cent; Entamoeba histolytica, in 16 per cent; Stronhyloides stercoralis, in 7 per cent; Giardia lamblia, in 5 per cent; and Hymenolepis diminuta, in 0.5 per cent. The aim of the survey was to gather baseline data on parasite prevalence before the Pan American Highway passes through this area. Construction of the highway is producing marked environmental change. in eastern Panama, and it is anticipated that the date from the survey will prove useful in later efforts to assess the health impact of that change.