Haemolymph samples from different Tridacnid clams were tested for haemagglutinin activity, using normal and enzyme-treated red cells from different sources. 2. Precipitin reactions with these haemolymph fluids were performed in agar gel, using several defined glycosubstances of different origin. 3. In several experiments it could be demonstrated that in all Tridacnid haemolymph samples anti-galactosyl ("anti-galactan") specific lectins do occur, however, they definitely differ from each other.