A new electrophoretic migration type of alkaline phosphatase 1 (Akp1) was found on the cellulose acetate electrophoresis for kidney and liver homogenates of KWHM mouse, a newly established inbred strain derived from the Korean wild mouse (Mus musculus molossinus). This new type of alkaline phosphatase 1 was distinguished from previously reported AKP1A and AKP1B types in the mouse, and tentatively named AKP1C. In genetic analysis by mating experiments between KWHM and C57BL/6J (AKP1A) or BALB/cA (AKP1B), the phenotypic segregation ratios of AKP1A : AKP1AC : AKP1C or AKP1B : AKP1BC : AKP1C were 1 : 2 : 1 in both groups of F2 generations. It was therefore concluded that AKP1C type is controlled by Akp1c allele which is codominant with Akp1a and Akp1b alleles.