A procedure permitting the simple determination of the O-2 and CO2 permeance of pouches used to pack respiring foods under real conditions is described. It is based on the measurement of the atmosphere changes in pouches tilled with a gas mixture whose composition is calculated as a function of the permselectivity of film. The experimental curves (p(CO2) and p((21-O2))) versus storage duration are submitted to an exponential regression. The exponential coefficients are directly proportional to the O-2 and CO2 permeances of the films. The method is designed for microperforated films (pen m selectivity close to 1), but can also be used to approximate the permeances of non-perforated films. The large variability of the permeances of the microperforated films is due to the heterogeneity of perforation density and diameter. © 2004 Elsevier B. V. All rights reserved.