An analytical method for the determination of nicotine has been established. It is a modification of an earlier reported method in which the over-all recovery of added nicotine has been increased from 55 to over 80 per cent. The determination is carried out by gas-liquid chromatography and the identity of the nicotine peak has been confirmed by mass spectrometry. The method has been applied to the determination of nicotine in the blood of cigarette smokers, and concentrations at the level of 1 ng ml–1 can be measured.