Although a number of reports on human blood acetaldehyde have been published, most of them during alcohol intoxication are still various in each researcher. The difficult problems are summarized as follows; 1) low boiling point of acetaldehyde, 2) low level in blood, 3) rapid disappearance in blood, and 4) artefactual formation during the procedures. The most crucial problem is the artefactual formation from ethanol or other sources during the procedures. Hemolysation, heating and/or other analytical procedures cause the artefacts. In this report, several methods for the determination and the evaluation of the acetaldehyde levels are reviewed.