A simple method of detecting polymorphism of S locus glycoprotein gene, SLG, in Chinese cabbage and cabbage was developed, and used for identification of breeding lines. DNA was amplified by the polymerase chain reaction (PCR) with a pair of primers having S 6 SLG sequences from inbred lines, and digested with restriction endonucleases which recognize tetranucleotide sequences. The cleaved DNA fragments were size-fractionated by polyacrylamide gel electrophoresis and detected by silver staining. PCR with S 6 SLG primers amplified a fragment of ca. 1.3kb in more than half of the inbred lines tested. After digestion, polyacrylamide gel electrophoresis revealed polymorphism between the amplified 1.3kb DNA fragments. These polymorphic bands were detected by Southern hybridization using a probe of S 6 SLG cDNA, suggesting that the amplified DNA was SLG. Primers having the SLG sequences of S 2 , a representative of recessive S alleles, were used for amplification of SLG in the lines which did not give the 1.3kb DNA fragment by the PCR with S 6 SLG primers. Polymorphism of amplified DNA was found in these lines. However these primers also appeared to amplify an invariant SLR-2 sequence of 1.3kb in addition to the polymorphic S 2 SLG related sequences. Although the used primer sequences still need improvement for the analysis of recessive S alleles, PCR-RFLP of SLG was considered to be useful for identification of breeding lines as well as for S allele identification in cruciferous vegetables. F1 hybrids exhibited the sum of the bands of both parents, and, therefore, this method is expected to be used for a purity test of F1 seeds.