Acid phosphatase activities were analyzed in ㎍ tissue samples from an angiosperm parasite (Cuscuta cephalanthi) and its host plant (Hedera helix) by a fluorometric microtechnique. The apex and the coiling portion of the parasite axis exhibited greater enzyme activies than other portions of the hypha. Acid phosphatase activity in the haustorium was 2-3 times that in the hyphal axis. The vascular bundles of the normal host exhibited the greatest enzyme activity. The acid phosphatase activity in the host infected by the parasite decreased to the activity level of the haustorium.