In this paper the Authors describe the presence of HIV particles on and in mature spermatozoa either ejaculated by AIDS patients or incubated in vitro with HIV. Both kinds of spermatozoa have particles localized around the sperm organelles. In the first case, the nucleoid of the virus can be enveloped by a membrane-like coat or be devoid of it and form buddings in the plasma membrane. In the in vitro infected spermatozoa, only membrane enveloped nucleoids are present, and no process of budding can be found. The Authors conclude considering that the spermatozoa of the AIDS patients can be penetrated by the virus particles in different moments of their life, and show the HIV particles in different stages of their cycle: some of them have freshly penetrated the sperm, and are still contained in a membrane-like coat, others are replicated and are budding through the sperm plasma membrane. On the contrary, in vitro infected spermatozoa have only freshly penetrated virus particles, and lack buddings and membrane-free nucleoids. The presence of the HIV virus in spermatozoa is substantiated by labelling with monoclonal or polyclonal anti-HIV antibodies.