Recently, we discovered the missense mutations of T to G at position 59 and of G to A at position 508 in one of the Lewis-negative (le) genes (Koda et al. 1993). In the present study, we report a method to detect the mutation at position 59 using mismatch PCR amplification and endonuclease MspI digestion. For this mutation, we found that 7 out of 12 Lewis-negative, and none of 15 Lewis-positive individuals were homozygous, while 4 out of 12 Lewis-negative, and 4 out of 15 Lewis-positive individuals were heterozygous. These results indicate that the mutation at position 59 is a common mutation in the le genes.