The human CD20(B1) gene encodes a B lymphocyte-specific cell surface molecule that is involved in B cell activation and differentiation. We described the restriction fragment length polymorphism (RFLP) of the CD20 gene in Korean population by Southern blotting and digoxigenin-labeling method, using 2.1 kb fragment (pB1-21A-29) isolated from the cDNA clone pB1-21 as a probe. The RFLP results with MspI showed a simple two-allele polymorphism with the band at either 9.0 kb (M1 allele) or 6.0 kb (M2 allele). Allele frequencies estimated from 114 unrelated Koreans were 0.47 for M1 allele and 0.53 for M2, respectively. the polymorphism information content (PIC) of the MspI RFLP was calculated as 0.37. Also, the result of chi-square analysis revealed no significant deviation of the MspI genotypic frequencies from the Hardy-Weinberg equilibrium(χ2=0.027, P>0.95). When the present study was compared with the previous data of Caucasian, the distribution of the allele frequencies was very similar between the two populations. From these results, we suggest that this RFLP of the human CD20 gene could be utilized as a basic datum to investigate the region of chromosome 11q which is known to be involved in some malignant human B cell disease.