We conducted comprehensive sequence analysis of 5' flanking regions of primate Alu elements. Information contents were computed and frequencies of 1024 pentanucleotides were measured to approximate the location of a characteristic sequence and to specify its pattern(s), which may be involved in the integration of Alu elements into their host genomes. A large number of samples was used, the wide region of the 5' end of Alu elements was analyzed, and comparisons were made among different subfamilies. Through our analyses, "TTTTAAAAA" or "(T)(m)(A)(n)" can be stated as a candidate for the characteristic sequence pattern, which resides around the region 5 to 20 base pairs upstream of the 5' end of Alu elements. This characteristic sequence pattern was more prominent in the sequences of younger Alus, which is a strong indication that the sequence pattern has a role at the time of Alu integration.