The ability of the human immunodeficiency virus (HIV) to persist and replicate in human CD4+ T lymphocytes and mononuclear phagocytes is under the control of both virally encoded proteins and a variety of host-related factors. Ultraviolet (UV) light has been shown to induce transcription and expression of HIV. Both DNA damage and repair and DNA damage/repair-independent pathways caused by UV irradiation lead to expression of proviral HIV genomes via activation of the cellular transcription factor NF-kappa B. Transgenic mice that contain either long terminal repeat (LTR)-reporter genes or HIV genomes, either full length or deleted in the gag-pol region, express RNA and proteins at the epidermal level, particularly after UV irradiation. Furthermore, UV-triggered release of soluble factors capable of inducing expression of HIV in non-irradiated cells has been observed. Among other host factors, the functional network of pro-inflammatory and immunoregulatory cytokines has been demonstrated to act as a potent regulator of HIV replication, at least in different in vitro systems of infection.