The effect of smoking tobacco upon perceptual selection, using the method of paced observing-responses, was studied in 15 habitual smokers. Subjects sampled each channel of a three-channel display for the presence of a signal at a rate of 1/1.5 sec. Average signal rate was 1/6 sampling epochs. Signal probability on the three channels was 0.6, 0.3 and 0.1. Subjects were tested after smoking no cigarettes, one cigarette and two cigarettes, and heart-rate was measured. Both total number of observations made and the proportion of observations made on the channel with highest signal probability showed an effect of prior smoking. Following no smoking, both of these scores increased during the test. ***Following smoking, the increase did not occur. It is suggested that smoking lowered arousal towards the end of the test.