In this paper, the results of chemo-toxicological examinations of post-mortem material taken from a man who committed suicide by carbon monoxide poisoning after earlier taking zopiclone are presented. The source of the carbon monoxide was exhaust fumes from a car in a closed garage. Tests carried out revealed not only a small amount of the medicine in its unchanged form (90 ng/ml in blood), but also its metabolite, N-dimethyl-zopiclone, which, as the dominant form in biological extracts, can constitute the main marker of drug intake in toxicological screening analyses.