Sulfite inhibited α-amylase activity of saliva, Asp. fumigatus. hen serum and mouse serum. Addition of sulfite to the enzymatic reaction system had no effect on the amylase activity. Pre-incubation time was necessary for inhibition of salivary amylase with sulfite. The enzyme inhibited with sulfite was reactivated by addition of an activator such as NaCl and the enzyme activated with NaCl was inhibited by the addition of inhibitor such as sulfite. With the addition of hydroquinone inhibition of enzyme with sulfite stopped. Immunological reaction between anti-salivary amylase serum and sulfite-enzyme or native enzyme had no effect on the quantitative precipitin and agar diffusion. Administration of sulfite had no effect on blood amylase activity under several in vivo conditions.