Human CYP4B1 is a CYP4 enzyme with activity towards xenobiotics. Five alleles of human CYP4B1 have been identified in French Caucasians, but allelic variants of enzyme have not been determined in the Japanese population. To establish a rapid and sensitive means of detecting variant CYP4B1 alleles, we analyzed those of 192 Japanese individuals using denaturing HPLC (DHPLC). We then determined the optimal conditions required to detect SNPs for each PCR fragment. Analysis by DHPLC revealed the novel alleles, CYP4B1(*)6 (517C>T and 1033G>A) and CYP4B1(*)7 (AT881-882-del, 993G>A, and 1018C>T), as well as 3 known alleles. The frequencies of the CYP4B1(*)1, (*)2, (*)3, (*)4, (*)5, (*)6, and (*)7 alleles in 192 Japanese individuals were 0.490, 0.328, 0.154, 0, 0.016, 0.008, and 0.005, respectively. The allele frequencies among Japanese relative to those in French Caucasians for CYP4B1(*)1 (0.490 vs. 0.724) and CYP4B1(*)2 (0.328 vs. 0.147) significantly differed. Our results suggest that high throughput DHPLC can rapidly detect pharmacologically important variants in CYP genes.