Three groups of rabbits of different origin (29, 27 and 28 animals; 3 or 4 - 6 months of age) were slaughtered, their caecal contents analyzed and used for inoculation of in vitro cultures. Whereas the caecal pH, dry matter percentages and acetate molar proportions in caecal volatile fatty acids (VFA) were relatively stable, molar proportions of other VFA varied considerably. In in vitro incubations, caecal parameters varied somewhat less than in vivo. Methane production varied much more than total VFA production. No non-methanogenic rabbit, however, was found. The hydrogen recovery correlated significantly with the methane production and, in two out of three groups of rabbits, also with the propionate molar percentage. The caecal pH was inversely related to VFA concentration.