AIDS is caused by the human immunodeficiency virus type 1 (HIV-1). Recent methods have been developed to estimate infectious titer in various bodily fluids, including blood. However, lack of information about HIV-1 stability in blood has restricted the use of these techniques to fresh samples in immediately accessible virology laboratories. In studies of infectious virus decay, it was found that at room temperature, complete decay of infectious HIV-1 in plasma can require > 7 days. Furthermore, the stability of HIV-1 was enhanced by storage at 4 degrees C, suggesting that fresh plasma could be sent on ice to core laboratories for viral quantitation. These studies also emphasize the need for thorough decontamination of all potentially infectious material.