This paper examines cultural and social meanings associated with semen, along with related issues of unprotected receptive anal intercourse, HIV seroconversion, treatment optimism and viraemia. The findings are derived from qualitative interviews conducted with 12 HIV-positive young gay men and 12 HIV-negative counterparts who participated in a prospective cohort study in Vancouver, Canada. Focussing on the narratives of young gay men, the analysis reveals a diverse range of knowledge, values and functions of semen, especially in relation to its exchange. Beliefs about semen appeared to differ by HIV serostatus and were linked with intimacy, identity and pleasure, particularly among the HIV-positive men. Against dominant representations of semen in relation to issues of loss, anxiety and infertility, this unique study sheds much needed light on its role within the cultural construction of sexuality among gay men. As such, these narratives are of direct importance to primary and secondary HIV prevention, including condom promotion and the development of rectal microbicides.