A method for starting up a system for oxidating organic bodies. The system includes a tubular body wherein an aqueous body is injected into the inlet thereof at a pressure P1, the tubular body having a first zone extending the inlet thereof, a second zone into which an oxidating compound can be injected into the output thereof. The inventive method includes the following steps: a first amount of thermal energy Q1 is provided in the first zone, the amount of thermal energy being able to raise the temperature of the liquid flowing through the tubular body from an initial temperature to a higher temperature T1; and a determined amount of a combustible mixture which can react at the intermediate temperature T1 in order to provide an amount of thermal energy Q2 bringing the temperature of the liquid to a reaction temperature T2 is injected.