The purposes of our study were (1) to investigate whether a 3-min short-term hyperventilation leads to posthyperventilatory hypoxemia and (2) to assess the role of transcutaneous blood gas measurements for monitoring oxygen and carbon dioxide changes during the after the test. In 10 male volunteers arterial and transcutaneous blood gases were measured simultaneously before, during and after a 3-min voluntary hyperventilation maneuver. Baseline arterial PO2 increased from 13.7 +/- 0.4 kPa (103 +/- 3 mm Hg) to 18.6 +/- 0.3 kPa (139 +/- 2.3 mm Hg; p < 0.005 compared to baseline) during hyperventilation. After the provocation test posthyperventilatory hypoxemia occurred with a minimal mean value of 7.8 +/- 1.3 kPa (58.5 +/- 9.8 mm Hg; p < 0.05 compared to baseline). Whereas close agreement between arterial and transcutaneous measurements was obtained for carbon dioxide values before hyperventilation, transcutaneous O2 consistently underestimated arterial O2. A short-term over-breathing of 3 min causes a significant posthyperventilatory hypoxemia. We hypothesize that posthyperventilatory hypoxemia is caused by hypopnea as a result of depleted CO2 body stores. Noninvasive transcutaneous blood gas measurements are not reliable for monitoring blood gas changes during and after hyperventilation, most probably because of the slow response time of the electrodes and the reflex vasoconstriction of the skin vessels.