A new, more sensitive HIV test uses microspheres to capture antibodies indicating infection. Because it can measure much smaller amounts of antibodies to the virus, the Bio-Plex Suspension Array System test may help more accurately determine the efficacy of vaccines in development. Researchers compared the new test to the ELISA (enzyme-linked immuno-sorbent assay), which has been the standard test for decades, in the two tests' abilities to detect simian immunodeficiency virus (SIV) in SIV-infected rhesus macaques. The microsphere-based test was able to accurately detect four important HIV antibodies in the monkeys, when compared with uninfected control animals. Also, it had enough increased sensitivity to ferret out the virus in instances where the ELISA provided a false negative for one or more of the antibodies.