In a process for measuring partial transcutaneous CO.sub.2 pressure on an earlobe by means of a sensor having a measuring device for measuring the partial transcutaneous CO.sub.2 pressure and a heating system for heating a sensor contact surface for contact with the earlobe, the sensor contact surface is heated. During a first phase, the sensor contact surface is kept at an elevated temperature of at least 41.5.degree. C. in order to prevent the measured value of partial transcutaneous CO.sub.2 pressure from exceeding, due to the measurement process itself, the partial transcutaneous CO.sub.2 pressure achieved after stabilization. The temperature of the sensor contact surface is then reduced to between 37.degree. C. and 41.degree. C. This facilitates considerably faster evaluation of the measured values.