Restriction fragment length polymorphisms were studied among the Japanese population using 12 polymorphic DNA probes on the q24-q28 region of X chromosome. The frequency distribution for probes p22-33, p482.6a, p43-15, 52A, pPM101, cX33.2 and cpx234, was the same as that for Caucasians, and that for probes 4D-8 and St14-1 (MspI) was slightly different (p less than 0.05). However, it was quite different (p less than 0.01) for probes p114.12, St14-1 (TaqI), 36B-2 and MN12. Probe p114.12 showed no HindIII polymorphism for the Japanese people. On the contrary, probe MN12, which has a low PIC value (0.15) for Caucasians, was found to be useful for Japanese (PIC value = 0.50). These results suggest that 7 DNA probes (p482.6a, p43-15, 52A, St14-1, p114.12 (BclI), 36B-2 and MN12) are useful (PIC greater than 0.42) for linkage analysis of X-linked disease in Japan.