INTRODUCTION Humidification of inspired gas in artificially ventilated patients positively influences mucociliary function and secretolysis. We performed this study to examine the properties of heat and moisture exchangers in comparison with hot water humidifiers and dry artificial ventilation. METHODS We measured inspired humidity with a special sensor in 41 patients after coronary artery bypass grafting with cardiopulmonary bypass. Three Heat and Moisture Exchangers (HME) and a hot water humidifier were used to humidity the inspired gas of artificially ventilated patients. Humidity measurements were compared. RESULTS Hot water humidifiers produced the highest humidification (average of 38.4 mg/l, 37-43 mg/l); lowest humidification was produced by dry artificial ventilation (average of 8.7 mg/l, 6-11 mg/l). Heat and moisture exchangers (HME) produced humidity between 24 and 36 mg/l. Highest humidification was produced by HME hygrobac s (average of 32.2 mg/l, 31-36 mg/l) and hygrovent s (average of 31.4 mg/l, 29-35 mg/l); lowest humidification was produced by HME hygroster (average of 28.6 mg/l, 24-31 mg/l). Multifactorial analysis shows a significant impact of the humidification method on the humidity of inspired gas. The multiple comparison procedure (Tukey) shows significant differences (alpha = 0.05) between all humidification techniques on inspired gas except the heat and moisture exchangers hygrobac s and hygrovent s. CONCLUSIONS Hygrobac s and hygrovent s may be an alternative to hot water humidifiers. Further clinical studies of HMEs and hot water humidifiers will be necessary to evaluate the influence of inspired gas humidity on the outcome of artificially ventilated patients.