The crucial genes for spermatogenesis have not yet been identified, but the AZF regions in the Y chromosome are now thought to show a major correlation with spermatogenesis. Recently, a complex of palindromes exists in the Yq, and is conserved in a highly repetitive sequence. Therefore, the PCR based sequence tagged site (STS) could not be accurately decided their unique position. This review demonstrated that there was not a high frequency of deletion of AZF-specific genes than expected using usual STS-PCR. However, the frequency of expression in AZF genes is relatively low. This discrepancy is probably due to repetitive sequence of complex palindromes in the Yq.