An oxygen tension measurement equipment, developed for continuous intravascular monitoring was tested as a direct tissue oxygen tension meter. The sterile disposable oxygen probe consists of a Clark type polaro-graphic bipolar electrode placed in a 5 cm long flexible polyethylene catheter (OD 0.55 mm). The probe is easily placed, e.g. in subcutaneous tissue or muscle, with the aid of an introduction needle. In vitro measurements as well as subcutaneous and intramuscular readings were performed. The animals were subjected to various experimental conditions such as different inspiratory oxygen fractions, hypovolemia, and circulatory impairment. Results were comparable to those obtained with previously used and well characterized tissue oxygen tension measurement equipment. The clinical applicability of the oxygen sensor for tissue oxygen measurement was assessed in one patient by 40 hours' surveillance in a free myocutaneous flap. The procedure was simple and implied minimal discomfort for the patient.