In the Japanese medaka, Oryzias latipes, 227 informative random amplified polymorphic DNA markers were detected. Segregations of a total of 170 loci, which included three pigment-pattern loci, five enzyme-coding loci, and one male-determining factor, were examined using intraspecific backcrosses of three inbred strains, two of which were highly polymorphic with respect to the remaining strain. The results were used to prepare a genetic linkage map of and medaka. The map consists of 28 linkage groups and spans about 2480 contiguous centimorgans (cM) with an average of 323 kilobase pairs (kb)/cM.