The results of a previous study indicated that, in the province of KwaZulu-Natal, South Africa, Necator americanus and Strongyloides stercoralis were endemic to the coastal lowlands only. The prevalences of these helminths, as well as those of Trichuris trichiura and Ascaris lumbricoides, have now been investigated along a 1000-km-long transect through the coastal plain, at altitudes of < 300 m, from the Mozambique border (26 degrees 57'S) to the border with Eastern Cape province (30 degrees 53'S). Necator americanus was by far the most dominant hookworm species. Although prevalences of N. americanus and S. stercoralis infection decreased with increasing southerly latitude, those of T. trichiura and A. lumbricoides did not. Determinants of these distribution patterns are examined in terms of a suite of temperature- and rainfall-related variables.