Transcutaneous Po2 (tcPo2) monitoring has become a reliable adjunct in the care of the critically ill neonate.1 The heated electrode applied to the skin produces local hyperthermia and vasodilation, "arterializing" the capillary bed under the electrode. Huch et al1 have noted no skin damage or irritation from hyperthermia for up to seven hours of application. However, others have noted lesions ranging from slight erythema to small vesicles, persisting from several hours to several days.2-4 Bossi et al5 noted erythema disappearing within 24 hours in every patient. To define the incidence and severity of these lesions we prospectively studied this aspect in infants undergoing tcPo2 monitoring.