The prevalence of sexually transmitted herpes simplex virus type 2 infection is increasing. Current prevention strategies are not successful. The majority of sexual transmission events in the US appear to occur during episodes of asymptomatic or unrecognized viral shedding. A series of studies to describe asymptomatic shedding, led by Drs Wald and Corey, will be summarized in the talk. Asymptomatic shedding occurs more frequently in the first few years after primary genital herpes and declines with time. Herpes simplex type 1, which causes an increasing proportion of genital HSV infections, is less frequently shed than is HSV type 2. The rate of shedding among men is similar to that of women. There is a positive correlation between symptomatic and asymptomatic reactivation: persons with frequent recurrences also have more asymptomatic shedding. Suppressive antiviral therapy very significantly reduces asymptomatic as well as symptomatic shedding as measured by culture or PCR. An ongoing study is addressing the possible effect of suppressive therapy on HSV transmission in disparate couples. Education concerning asymptomatic shedding, and possibly suppression of such shedding, may be effective HSV control strategies. Vaccination is another attractive control technique, but has been difficult to achieve due to incomplete understanding of protective immunity in humans. Our cellular immunity lab studies will be briefly summarized to highlight data that could direct future vaccine design strategies.