Cigarette-induced changes in heart rate, skin temperature and subjective state were measured during the course of a normal smoking day and on smoking after 24 h abstinence in 21 smokers. Heart rate was not affected by smoking a test cigarette during the normal day's smoking, but after 24 h abstinence smoking a cigarette caused an average increase of 14 beats per min. Skin temperature, on the other hand, was reduced by smoking a cigarette under both conditions. Subjective effects of smoking were experienced only after the period of abstinence. The most common was dizziness, but nausea and other effects were also reported. Cigarette-induced changes in heart rate and skin temperature were positively correlated with each other, and the rise in heart rate after abstinence correlated positively with the strength of the subjective response. The results are discussed in terms of similarities and differences between different physiological systems in tolerance to the effects of nicotine.