Children aged between 1 month and 10 years from one rural coastal locality, two rural upland localities and two urban localities in Morobe Province, Papua New Guinea were examined between September 1980 and September 1982. Hookworm (predominantly Necator americanus), Ascaris lumbricoides and Trichuris trichiura increased in prevalence with age. The prevalence of Strongyloides fuelleborni subspecies kellyi, where present, was either highest in the < 1 year age group or similar in all age groups. N. americanus prevalence was between 59% and 83% in the 3 year age group except at the coastal locality, where it was 15%. A. lumbricoides prevalence in the 3 year age group was very low in one upland locality and between 7% and 41% for the other localities. T. trichiura prevalence in the 3 year age group was between 33% and 55% at the coastal and two urban localities, and very low at the two upland localities. S. f. kellyi prevalence in the < 1 year age group was 48% and 20% respectively at the two upland localities, 2% at one of the urban localities and not detected at the other localities. Strongyloides stercoralis was detected at both urban localities, but not at the coastal locality or at the upland locality where testing was done. Many children had infections of more than one species, and there was a significant association of A. lumbricoides with T. trichiura at the coastal and two urban localities. The presence of S. f. kellyi at one of the urban localities raises the possibility that this once isolated species may now be spreading as infected people visit and settle in the towns. Between 68% and 93% of children in the 3 year age group and between 65% and 100% in the 5 year age group were infected with at least one helminth species.