Restriction fragment length variations (RFLVs) were investigated for increasing genetic markers for drawing autosomal linkage maps in Japanese quail (Coturnix japonica). The best tissue for extracting genomic DNA from this species was lung in adults and brain in newly hatched chicks, respectively. For digesting DNA at the optimum temperature of 37ﾟC, the following 12 low-priced restriction enzymes were selected: Apa I, EcoR I, Pst I, BamH I, Hind I, Kpn I, EcoR I, Dra I, Pvu II, Xba I, Bgl II, Sac I. As probes, many random genomic clones were produced from the liver extract of a quail. Out of them, 12 probes were selected and were numbered consecutively for use. Six families composed of parents and their offspring with the information on sex and 17 autosomal genetic marker loci (seven plumage color loci, two eggshell color loci, and eight biochemical loci) were selected, Two sex-linked probes were detected. These are probes No.1 and No.3, which detected RFLVs in DNA digested with Pst I and EcoR I, respectively. From two families, these probes were clarified to be on Z chromosome. These probes will be useful for expanding genetic map on Z chromosome in Japanese quail and for studying the homology of Z chromosome in the chicken belonging the same family. No autosomal probes could not be detected from the above six families in spite of the use of many restriction enzymes. In future, more families will be investigated for detecting autosomal probes. No evidence of autosomal close linkage was detected among the 27 pairwise combinations including seven plumage color and six biochemical loci. Two new mutations were detected. One is named "celadon", which is an autosomal recessive eggshell color mutation. The other is called "light down", that is an autosomal dominant plumage color mutation with homozygous lethality. These mutations will be useful as new genetic markers for expanding linkage maps.