Nonexponential losses of activity in alkaline phosphatase were observed with four substrates after gamma -irradiation. Those losses were at the same rates for each of the combinations of radicals generated in water under O/sub 2/, N/sub 2/, and N/sub 2/O. However, the composi tions of the radiolysed proteins varied depending on the gaseous atmosphere used. The enzyme retained a high proportion of its activity even when extensilie radiolytic damage to its component residues was found. These data suggest that radical attack on the phosphatase was at centers of secondary importance for the enzymatic activity. (auth)