The effects of rapid smoking, casual smoking, and rapid breathing on heart rate, blood pressure, cardiac output, and rectal-forearm-finger temperatures were compared. Carboxyhemoglobin, end-tidal carbon monoxide, plasma nicotine, electrocardiogram, and subjective symptom data were also obtained during these conditions as an older subject group smoked low nicotine cigarettes and younger subject groups smoked either high or low nicotine cigarettes. The authors concluded that the physiological changes produced by rapid smoking are greater than those produced by casual smoking and are not an artifact of rapid breathing. The controversy concerning the hazard potential of rapid smoking for either young or older subjects, however, is not fully resolved.