Saliva.

Though HIV is sometimes present in saliva, it apparently exists at very low concentrations. HIV can be in saliva because saliva contains T-cells and macrophages, which rove around the surfaces of the mouth's mucous membrane. The concentration of HIVs in saliva seems to be very low compared to blood and semen.

In theory, saliva can transmit HIV infection but, so far, it doesn't seem to have happened in real life. Kissing is discussed in more detail in the next section.