Abstract : In order to check the heterogeneity of the CI chondrites and determine the average composition of this group of meteorites, we analyzed a series of six large chips (weighing between 0.6 and 1.2 g) of Orgueil prepared from five different stones. In addition, one sample from each of Ivuna and Alais was analyzed. Although the sizes of the chips used in this study were "large", our results show evidence for minor chemical heterogeneity in Orgueil, particularly for alkali elements and U. After removal of one outlier sample, the spread of the results is considerably reduced. For most of the 46 elements analyzed in this study, the average composition calculated for Orgueil is in very good agreement with previous CI estimates. This average, obtained with a "large" mass of samples, is analytically homogeneous and is suitable for normalization purposes. Finally, the Cu and Zn isotopic ratios are homogeneously distributed within the CI parent body with a spread of less than 100 ppm per atomic mass unit (amu).