Synthetic benzylisoquine compound D₂₀ exibites stronger inhibition on CaM-activatedphosphodiesterase than TFP.IC₅₀=5μmol/L.Flourescence analysis indicats that the asso-ciation constant (K_a) for the interaction between CaM and compound D₂₀ is 2.64(μmol/L)^-1 and compound D₂₀ molecule possesses 2 binding sites for CaM.Binding style is discussed.