Squirrel monkey retrovirus (SMRV) is an endogenous type D retrovirus of the squirrel monkey, a New World primate. Southern hybridization with cloned SMRV-H revealed that 3040 copies of SMRV proviral DNA are present in the squirrel monkey genome and the majority have almost the same physical map as that of the cloned SMRV-H. SMRV-related sequences in the human genome were sought using the same method with various cloned SMRV-H DNA fragments under conditions of relaxed stringency. The discrete restriction fragments were frequently detected in the DNA from normal humans with the LTR and parts of gag and env as probes. Since SMRV LTR has very little homology with the LTRs of other retroviruses, the fragments detected with the LTR probe were characterized as SMRV-related human sequences. SMRV LTR-related sequences were also detected in the African green monkey and chicken, but not in the salmon, mouse, or dog. In conclusion, SMRV-related sequences are present in human DNA, and some of them might represent endogenous retroviral sequences of human DNA.