Abstract
Spores were irradiated and their E.S.R. signals studied. The radiation-produced radicals fall into six distinct groups, only one of which reacts with O2. The groups were characterized by their behaviour in N2, O2 and NO. These gases were chosen for their ability to modify biological radiation damage. In control experiments with unirradiated spores the endogenous radical populations were examined. Surface radicals were observed which react reversibly with O2, NO and NO2.