A new cell expression test, known as the gp120 Tagger method, introduced by Bio-Tech Imaging, Inc., is a new technol. to detect and count the productively infected cells in which HIV-1 is multiplying.The detection happens within 24-72 h of the initial onset of the infection and it uses specific monoclonal antibodies to identify productively infected cells.Studies using this technique indicate that tagging and separation are 99% accurate when infected cells are present in in vitro samples.This technique has fewer steps and requires less time than other direct or indirect methods, and is useful for samples of body fluids other than whole blood.