Sequences related to the squirrel monkey retrovirus (SMRV) LTR were isolated from a genomic library of human DNA by screening under conditions of relaxed stringency. The probe contains several transcriptional signals and its regulatory sequences in SMRV-H LTR, such as the enhancer sequence, CAT box, TATA box, and polyadenylation signal. More than 50 positive signals were detected in 4.4×105 recombinant phages. The cloned human sequences named SRH strongly hybridized with SMRV-H LTR and some of them weakly hybridized with SMRV-H structural genes. In SRH-1, the region related to SMRV-H prt-pol-env was flanked by the two separately located sequences related to the LTR. SRH-3 has a solitary LTR-related region, whereas, in SRH-5, the LTR-related region was adjacent to the pol-env-related sequence. The reliability of these hybridization experiments was confirmed by reciprocal hybridization. The restriction enzyme cleavage maps of these clones were different from those of known human endogenous retroviruses. Alu sequences, a human highly repetitive sequences, were inserted to the LTR-and pol-env-related regions in SRH-5.