The effect of zinc(II) and other metal ions on the catalytic activity of native and immobilized alkaline phosphatases isolated from three different sources (Escherichia coli, chicken intestine, and small intestine of Greenland seal) was studied. Zinc(II) inhibits the catalytic activity of all native alkaline phosphatases to different extents. Zinc(II) produces the most significant and selective effect only on the alkaline phosphatase from seal intestine. As for alkaline phosphatases immobilized on polyurethane foam, zinc(II) hardly affects the activity of the enzyme from chicken intestine and inhibits the phosphatases from E. coli and seal intestine in concentrations from 2.5 to 50 g/mL and 0.1 ng/mL to 50 g/mL, respectively. With the use of native and immobilized alkaline phosphatase from the small intestine of the seal, selective procedures were developed for the determination of Zn(II) with spectrophotometric and visual control of the reaction rate. The detection limits are 1 g/mL and 0.1 ng/mL, respectively.