Arterial hemoglobin oxygen saturation measured with the Datascope ACCUSAT pulse oximeter was compared with simultaneous arterial hemoglobin oxygen saturation measurements in healthy adult volunteers. One hundred thirty-five arterial blood samples ranging in saturation from 63 to 100% were obtained from 15 adults, aged 20 to 43 years. These subjects had different skin pigmentation, hematocrit, and smoking habits. Steady-state hypoxia was achieved by varying the inspired oxygen concentration between 10 and 21%. Readings from the Datascope ACCUSAT pulse oximeter and the Hewlett-Packard 47201A ear oximeter were compared with arterial blood samples analyzed by the Instrumentation Laboratories IL 282 in vitro CO-Oximeter. The equation for the best fitted linear regression line between the ACCUSAT pulse oximeter and the reference IL 282 CO-Oximeter was: ACCUSAT = 1.08(IL) - 6.86. The linear regression analysis revealed a high degree of correlation (r = 0.99), and a small standard error of the estimate (SEE = 1.29%). Simultaneous comparisons between arterial hemoglobin oxygen saturation measured with the ACCUSAT pulse oximeter and the Hewlett-Packard ear oximeter also showed a close correlation (r = 0.99, SEE = 1.47%). A similar comparison between the ACCUSAT and the Ohmeda 3700 pulse oximeter revealed good correlation (r = 0.99, SEE = 1.72%). We found that the ACCUSAT pulse oximeter is an accurate instrument for measuring arterial hemoglobin oxygen saturation noninvasively in the range between 60 and 100%.