Age-dependent changes of the caecal fermentation pattern were studied in female chickens using in vitro batch incubation technique. Chickens were sequentially killed at the age of 1, 2, 3 and 4 months, their caecal contents added to a broth with starch and incubated at 39 °C for 20 h. Net productions of short-chain fatty acids (SCFA), succinate, ethanol, lactate, methane, hydrogen and ammonia were determined. Methanogenesis was absent in caeca of 1-month-old chickens. Production of methane started in the second month and doubled in the third month of age. The start of methanogenesis was accompanied by changes of the fermentation stoichiometry. The production of succinate ceased and that of ethanol decreased to less than one tenth. There were no major changes of the caecal fermentation pattern in the fourth month of age. The ammonia production increased in the second month, indicating increased deamination activity. No major shifts in SCFA molar composition dependent on age were found. Calculated hydrogen recoveries suggest a decrease of reductive acetogenesis until 3 months of age. It can thus be concluded that age and the onset of methane production affect the fermentation pattern in the caeca of chickens.