The inheritance of three parameters of body size: body mass, hind femur length and pronotum length, and of three measurements of male fertility: testis mass, relative testis mass (as part of body mass) and sperm number per spermatophore, were examined in crosses between the bushcricket subspecies Poecilimon veluchianus veluchianus and P. v. minor. Body size parameters differed surprisingly in their apparent genetic control: the genes determining pronotum length were autosomal, hind femur length was probably partly X-chromosomal and body mass was largely determined by genes on the X-chromosome. I consider whether sexually selected traits may commonly be sex-linked. Testis mass in the hybrid males was clearly different in reciprocal hybrids and was similar to the father's subspecies in both cases. As a result of the X-chromosomal (maternal) inheritance of body mass and a testis mass similar to the paternal subspecies, the relative testis mass in the hybrid males was larger or smaller than in the pure subspecies. In the male hybrids with reduced testis mass, the mean number of sperm was strongly affected. About 50% of these males transferred only a few sperm per spermatophore.