Glycerophosphocholine phosphodiesterase release phosphocholine from resorufin phosphocholine to give the highly fluorescent resorufin that can be readily monitored by either fluorescence or absorption. This fluorogenic phosphodiesterase substrate can be conveniently used for screening the inhibitors of glycerophosphocholine phosphodiesterase. It can also be used for monitoring the activities of phospholipase D in combination with a phosphatase. Phospholipase D hydrolyzes resorufin phosphocholine to resorufin phosphate, which in the presence of an acid phosphatase generates resorufin. Thus, resorufin phosphocholine can also be used for monitoring phospholipase D in sources that do not also contain high levels of phospholipase C.