AbstractThe phosphodiesterase from calf spleen (EC 3.1.4.18) was immobilized on several supports. Some properties of the most suitable enzyme support system—calf spleen phosphodiesterase bound to agarose‐Concanavalin A—were investigated, e.g., pH dependence, influence of ionic strength of the buffer medium, and Zn2+‐ion inhibition. The immobilized spleen phosphodiesterase showed about 60% of the activity of the free enzyme: the activity toward several oligonucleotide test substrates was unchanged for two