Measuring the HIV-1 p24 antigen is a long-established method for lentivirus quantitation. However, the traditional p24 ELISA detects both virus-associated p24 and free p24 generated by 293 cells during transient transfection. Free p24 can account for a substantial portion of total p24 in the supernatant. Therefore, the ELISA typically overestimates the quantity of lentivirus present. Our QuickTiter™ Lentivirus Titer Kit (Lentivirus-Associated HIV p24) substantially minimizes this problem. A proprietary technology separates the lentivirus from free p24 in solution prior to running the ELISA portion of the assay.