We have isolated 8 different long terminal repeat (LTR) sequences of the ERV-H family of endogenous retrovirus-like elements from human chromosome 18, 9 from African green monkey, and 28 from marmoset. Human ERV-H LTRs have been divided into three types designated Type I, Type Ia, and Type II. Comparative analyses of the 45 isolated LTRs and 60 human ERV-H LTRs enabled a further subdivision into 13 subtypes. Type I elements were widely distributed in all three species. Their average evolutionary age (40 MYr), estimated by a consensus sequence approach, suggests that they first expanded in the genomes at the time New- and Old World monkeys diverged. The occurence of some very old Type I sequences indicate that ERV-H elements may have integrated even before prosimians and primates diverged. Type Ia and - II elements were found in both monkey species. Promoter active Type I and Type Ia LTRs were found while Type II LTRs were inactive. Promoter active Type I LTRs generally contained a functional GC/GT box immediately 3' to the TATA box, providing strong binding of Sp1 family proteins, while the highly promoter active Type Ia element H6 contained synergistically acting Sp1 binding sites located in the U3 enhancer region.