A continuously operated reactor was developed for the limited hydrolysis of whey protein using soluble trypsin. It consisted of a stirred tank followed by a tubular device. A stirred tank was used because it allowes pH control to be achieved more easily. The tubular reactor was applied in order to achieve a high level of conversion without pH control. The tubular reactor was equipped with static mixers for approximating plug-flow behaviour. The behaviour of the reaction system under floating pH in both parts of the reactor was evaluated separately prior to verification of the results in a pilot-plant which consisted of the combination reactor. The operating temperature and pH in the stirred tank were investigated as the main variables of the process.