Gamma-ray irradiation at 310 K induced formation of the peroxynitrite ion-ONOO- in solid alkali nitrates has been studied. In addition to the peroxynitrite ion one more product (which can be assumed to be the oxonitrate (1-) ion NO-) is determined by a permanganate potentiometric titration. The change of the total concentration of the two ions vs. the absorbed dose is of oscillation behaviour. The initial radiation yield of peroxynitrite and oxonitrate (1-) are equal to 0.03 +/- 0.01, 0.14 +/- 0.02, 0.78 +/- 0.09 and 1.46 +/- 0.20 (100 eV)(-1) in NaNO3, KNO3, RbNO3 and CsNO3, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.