Recent studies indicate that human immunodeficiency virus type 1 (HIV) gene expression can be dramatically enhanced by certain heterologous viral and chemical agents, implicating these as potential reactivating agents of latent virus infection. A common denominator shared by these agents is their ability to cause stress responses in cells. In an effort to determine whether stress responses affect HIV gene expression, we examined the effects of ultraviolet light (UV) and mitomycin C, on HIV gene expression as well as on viral growth and development. We demonstrate that these agents enhance HIV gene expression up to 150-fold. These levels are similar to those obtained by the tat gene product, the HIV trans-activating factor responsible for enhancing viral gene expression. The increase in gene expression after UV irradiation appears to require transcription but not de novo protein synthesis, and correlates with an accumulation of stable mRNA. Most importantly, UV irradiation of human T-cells prior to viral infection significantly shortens the viral growth cycle. Apparently, UV-induced cellular stress is highly conducive for viral replication and growth. We further demonstrate that even direct sunlight can activate HIV gene expression. These results demonstrate that DNA damaging agents, and perhaps other agents which elicit SOS-like stress responses in mammalian cells, can activate HIV expression thereby enhancing viral replication and development.