Abstract.The role of some adult flies (Diptera: Cyclorrhapha) as carriers of helminth parasites of man was studied at four sites in Malaysia: a refuse dump, where no helminth‐positive flies were detected, and in three peri‐domestic situations where four species of flies carried up to three types of nematodes.The dominant fly speciesChrysomya megacephala(Fabricius) carried eggs of the roundwormAscaris lumbricoidesL., the pinwormTrichuris trichiura(L.) and hookworm on the adult external body surface and in the gut lumen, in association with Bukit Lanjan aborigines.Chrysomya rufifacies(Macquart) andSarcophagaspp. also hadAscaris lumbricoidesandTrichurus trichiuraeggs in their gut contents. Human helminths were not recovered fromLispe leucospila(Wiedemann),Lucilia cuprina(Wiedemann) or the houseflyMusca domesticaL.In an urban slum area of Kuala Lumpur city, filariform larvae identified as the hookwormNecator americanus(Stiles) occurred in the intestines of the face‐flyMusca sorbensWiedemann (22 larvae per 100 flies) and ofChrysomya megacephala(4.5 larvae per 100 flies). This concentration of apparently infectiveN. americanusinM. sorbens, a fly which often breeds in faeces and browses on human skin, could have transmission pote