imb deformity was found in SPF KM stock,whichis due to the increaseof inbreeding coefficent after caeserean operation.The skeletal deformities ofKM-ld appear to be confined to the portions of limbs below the elbows andknees.The tibia and fibala and the ulne and radius are shorter than that ofnormalones,or replaced by single curved bones in soine homozygotes.Preaxialpolydactyly and syndactyly of hindfeet were also found in most KM-ld hom-ozygotes.Among 138 KM-ld mice,42% were combined with anomalies of lefturogenital system, including anephrogenesis,hydronephrosis and hydroureter inthe left side.Breeding analysis data are 21 :121 (X2 3.16) by intercrosses and14:27 ( X20.04 ) by backcrosses. Therefore,ld is autosome single gene recessiveinherited and KM-ld stock will be useful model in biomedical research.