Measuring virion infectivity is critical for studying and monitoring the process of HIV-1 infection. The easiest and the most common method utilizes reporter cell lines based on the HIV LTR promoter. The early HIV gene product Tat amplifies expression from the LTR; however, there is a background transcriptional activity that is independent of Tat. Furthermore, LTR activity can be influenced by cellular activation states. We have recently constructed a Rev-dependent expression vector, and as a test of this construct's functionality, we have integrated this vector into a continuous T cell line. This novel indicator cell has no measurable background signal, is not affected by elevated metabolic states, and yet responds robustly to the presence of HIV. The line is able to complete TCID50 assays in 3-5 days, and appears sensitive to both CCR5- and CXCR4-utilizing viruses.