This article describes experiments to quantify the link between temperature increase and radical concentration and the part played by alkyl peroxy radicals RO 2 in the kinetics of the low-temperature oxidation of n-heptane. The flow method is used, at atmospheric pressure, with two reactors, one of boric acid-coated Pyrex glass, and the other of stainless steel. The stabilized slow reaction and cool flame are studied by means of electron spin resonance (esr) and thermal measurements. When a slow reaction occurs the radical concentration and temperature prof'des versus distance have coincident maxima. For a slow reaction followed by a cool flame the profiles show a relative shift. The concentration maximum always precedes the temperature one and occurs when the temperature rise reaches approximately the critical value ATetit. In the flame (between ATerit and the temperature maximum) the RO 2 concentration decreases drastically. As a new explanation for the cool flame self-inhibition and hence periodicity, we propose a sequence of chain-breaking (or slowing down) reactions, between RO 2 and active centers produced by peroxide decomposition in the cool flame. tylhydroperoxides (C7H1502) in a dynamic