Arachidonoyl thio-PC is a substrate for cPLA2 by virtue of the presence of arachidonic acid at the sn-2 position of the glycerophospholipid. Hydrolysis of the arachidonoyl thioester bond at the sn-2 position by PLA2 releases free thiol which can be detected by DTNB. This assay can be used to determine the activity of cPLA2 in purified preparations, cell cultures, or tissue homogenates that are known to contain only cPLA2. Use of this assay with preparations containing more than one type of PLA2 will result in the measurement of total PLA2 activity rather than cPLA2 alone. Isozyme-specific cPLA2 activity can be measured by excluding sPLA2 or inhibiting iPLA2 activities in the assay.