An anomalous sex-chromosome constitution was observed by chance in a case of phenotypically normal female golden hamster. Bone marrow metaphases of this animal showed 44 chromosomes with a karyotype which was indistinguishable in general appearance from that of the normal male. Two tentative interpretations were made for the sex-determining mechanism of the present specimen: one is the XY constitution in which the Y chromosome had lost its male factors due to the interchange of genetic materials between the X and the Y at the time of meiotic segregation, and the other deals with a partial short arm deletion in one of the two X chromosomes.