1. The molecular weight of the native hemocyanin from Ampullaria canaliculata determined by gel filtration has a molecular mass of 7.5 x 10(6) Da. Dialysis against buffer free of Ca2+ and Mg2+ ions dissociated the hemocyanin into molecular species of 1.0 x 10(6) and 3.2 x 10(5) Da. 2. The oxygen-binding curves of hemocyanin were sigmoidal with Hill coefficient of about 2. A positive Bohr effect was demonstrable at pH values ranging from 6.5 to 9.0. 3. Differences between associated and dissociated hemocyanin as well as the effect of the divalent cations on the aggregation of hemocyanin molecule were illustrated by immunoelectrophoresis analysis. 4. Negatively stained preparations of hemocyanin observed by TEM showed the cylindrical configuration of molluscan hemocyanins molecules. Its inner structure, enhanced by the negative contrasting, reveals a regular periodicity as a result of the alignment of serial subunits.10541732725730