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The soil-transmitted helminths are the most common helmin- thic infections, affecting about one-fourth of the world’s population. There is a significant genetic component to susceptibility to infection with these organisms. Substantial changes in plasma cytokine levels are associated with helminthic infections, and there may be significant genetic components to this cytokine variation. Six plasma cytokine levels were assessed for 367 members of a single pedigree from the Jirel population of eastern Nepal. This population experiences moderate rates of infection with geohelminths. Sex, age, helminthic infection, infection with Giardia, and presence of a household latrine were considered as covariates in all analyses of the cyto- kine data. The analyses of the single Jirel pedigree revealed significant herita- bilities for IFN-� (h2 � 0.654 � 0.096), TNF-� (h2 � 0.458 � 0.101), IL-2 (h2 � 0.583 � 0.101), IL-4 (h2 � 0.700 � 0.095), IL-5 (h2 � 0.676 � 0.087), and IL-10 (h2 � 0.597 � 0.093). The ratios of IL-4 to IFN-� and of IL-10 to IFN-� were used as indicators of the degree of type 2 bias in immunological response; analyses of these variables indicated that approximately 40–60% of the variation (h2 � 0.400–0.577) in these derived measures of relative type 2/type 1 response is due to genetic factors.