The karyotypes of Gryllus rubens (Scudder) and Gryllus sp. collected in the US were studied using conventional Giemsa staining and two differential staining methods. Both species had a chromosome complement of 2n = 28 + XX/XO, and the X chromosome was large and metacentric. In addition, nucleolus organizer regions (NOR) were detected in the short arm of one pair in the two species, and the NOR showed variation in size. The two species had species-specific chromosome configuration and C-banding patterns. In Gryllus sp., the chromosome configuration showed polymorphism in size and type among individuals, and the distal C-bands of Gryllus sp. were larger than those of G. rubens.