Four pulse oximeters and two pulse oximeter-capnographs were evaluated on accuracy of measuring oxygen saturation and heartrate for the former and oxygen saturation, heartrate, respiratory rate and capnography for the latter. In the first part of the study four pulse oximeters (Criticare Systems Model 501 +, Ohmeda Biox 3700 Pulse Oximeter, Nellcor Model N 100 and Datex Satlite) were simultaneously studied on 10 ventilated ICU patients. Fifty simultaneous measurements were done for heartrate and oxygen saturation and compared to arterial saturations and ECG heartrates. Mean differences from pulse oximeter values versus control arterial and ECG values were within two percent for the four instruments. In the second part two oxicaps (Ohmeda 4700 and Nellcor N 1000) were evaluated with the same control parameters. Thirty measurements on 3 patients were done. As in the first part of the study all results were accurate within two percent of control values. From those data we can conclude that all examined monitors were fairly accurate compared to simultaneous arterial blood gas analysis and ECG monitoring. The oxicap monitors have the advantage of giving continuous information on two very important parameters of patient monitoring: CO2 and saturation.