Two newly established inbred strains derived from Mus musculus musculus, designated PWD/Ph (F29) and PWK/Ph (F33), were examined for their alleles at 37 biochemical loci located on 12 different chromosomes. The allelic pattern showed characteristic differences from those observed in common inbred strains. The genetic distance D between PWK/Ph and PWD/Ph was 0·027, whereas the corresponding values for the genetic distances between PWK/Ph and C57BL/6J, DBA/2J, BALB/cJ and SWR/J were 0·777, 0·721, 0·721 and 0·838 respectively. New allozymes are described as being controlled by the loci Es-23, Pre-2 and Tam-1. The genetic relationship to M.m. molossinus is indicated by identical alleles at six other loci ( Es-2, Es-9, Es-10, Es-11, Es-18 and Es-22).