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.