Isozyme and cytogenetic analyses were performed on selfed progenies of a synthetic amphidiploid between scarlet eggplant, Solanum integrifolium (= S. aethiopicum),and eggplant, Solanum melongena `DMP', for estimating genetic uniformity. Isozymes in the 379 examined seedlings segregated into five genotypes (phenotypes) each at the four loci examined, Pgd-2 of phosphogluconate dehydrogenase (E.C.1.1.1.43), Idh-2 of isocitrate dehydrogenase (E.C.1.1.1.41), Pgm-2 of phosphoglucomutase (E.C.2.7.5.1)and Skdh-1 of shikimate dehydrogenase (E.C.1.1.1.25), indicating that the selfed seedlings were not genetically uniform. Most of the examined 15 selfed seedlings exhibited a somatic chromosome number of 48, that is the same number of the synthetic amphidiploid, whereas isozyme genotypes among them were variable. It is suggested that the segregation of isozymes was not caused by variation of chromosome number but by genetic segregation of isozyme genes. The genome of the synthetic amphidiploid was indicated to be unstable.