A diallel analysis was used to estimate certain genetic parameters for soluble solids in tomatoes. All crosses of small- x small-fruited strains and some small- x large-fruited crosses showed heterosis in the F1 with the means exceeding the top parent. The genetic analysis indicated that epistasis or nonallelic gene interaction was primarily responsible for the heterosis. The experiment also demonstrated the existence of dominant genes for high solids. These genes were shown to have rather large effects. Evidence indicates that genes for high solids were contributed by the wild species Lycopersicon pimpinellifolium. A heritability estimate of .54±.07 was obtained for soluble solids.