This contract performs in vitro confirmatory testing of drug substances submitted to DAIDS for further development as potential anti-HIV therapies. The goal is to independently confirm the initial observation of anti-HIV activity of promising drug substances and then examine the spectrum of in vitro activity in multiple cell types against panels of laboratory and/or primary HIV isolates representing viruses with different co-receptor usage, clade classification, and/or drug sensitivity. In addition, potential drug-drug interactions shall be examined and drug-resistant HIV isolates shall be made for the most promising drug substances.