A newly developed Herpes simplex virus (HSV) type 1 and type 2 enzyme immunoassay has been applied to over 40,000 sera from different populations in the US and 17 other countries on all 5 continents. The HSV-1 antibody patterns found permit the current and past socioeconomic status, as well as the extent of oral-genital sexual contact, to be deduced for various populations. The HSV-2 antibody results provide an objective measure of various aspects of sexual behavior: extent of polypartnerism in the subjects tested (or their contacts), early age of sexual experience and acquisition rates of genital herpes. It has thus been possible to extend sero-epidemiology to sero-sociology which can provide objective markers for sexual behavior and effects of intervention or educational approaches. Besides such markers having potential applicability for monitoring other STDs, such as HIV infection, recent studies also support a possible role for HSV infections to increase the transmissibility, not only of HIV-1, but also of HTLV-1.