et d'l mmunologie, Thiverval-GrignonHomogenates prepared from the developmental stages of the nematodes, Nippostrongylus brasiliensis (a rat parasite) and Haemochus contortus (a sheep parasite) were found to react specifically with two myeloma sera that possess anti-phosphorylcholine binding activity. Some properties of the phosphorylbearing components and of the precipitation reaction are presented and the postulated biochemical nature of these components is discussed.