The feeding of rapidly fermentable, high energy, diets to young calves stimulates a rapid development of microbial fermentation. High concentrate diets may not, however, stimulate a corresponding development of salivary flow (Kay, 1966). A number of factors affect the buffering system of ruminal contents, besides saliva, such as the concentration of the end products of fermentation and the rate at which these products are absorbed through the rumen epithelium (Turner and Hodgetts, 1955). Counotte, van Klooster, van der Kuilen and Prins (1979) presented the analysis of the buffer system in the rumen using the first derivative of the titration curve. The results showed that bicarbonate and VFA are the main chemical components of the buffer system in the rumen fluid of adult dairy cattle. The ability to buffer against potentially large deterimental fluctuations, ie rumen pH, may improve rumen stability and be benefical to stimulate solid food intake in the early weaned calf. The present experiment describes a system for analysing the buffer system in the developing rumen of the young calf.