Muskmelons (Cucumis melo L.) are well-known as excellent sources of several vitamins, minerals and non-enzymatic antioxidant phytochemicals such as vitamin C and pro-vitamin A. Less well-studied is their potential role as sources of enzymatic antioxidants such as superoxide dismutase (SOD), which have been associated with enhanced reactive oxygen species scavenging capacity in some muskmelon fruits. In this study, we investigated the variability in SOD activities among diverse advanced breeding lines and commercial muskmelon cultivars grown in two different soil types-clay or sandy loam. Specific and total SOD activities varied significantly among the genotypes (P <or= 0.001), compared to soil type (P <or= 0.055). Netted (cantaloupe) genotypes generally had the lowest SOD activities compared to the green- and orange-fleshed honey dew types. Casaba type fruit had average SOD activities that were approximately 1.6-fold greater than those of honey dew types, and approximately 9.0-fold greater than those of cantaloupe types. These data indicate there is useful genetic diversity among commercial melon varieties and in exotic genotypes that could be used to develop C. melo as a functional food with enhanced SOD content.