Forty subjects were exposed to cigarette smoke produced by a smoking machine in a climatic chamber. The degree of air pollution due to cigarette smoke corresponded to 2.5 and 1.3 ppm delta CO. The concentrations of particulate matter, NO and NO2, were measured. The effects on subjective irritation, annoyance and eye blinking rate were determined. All measured effects increased with increasing smoke concentration as well as with exposure duration. Based on these effects, a tolerable limit in the range between 1.5 and 2.0 ppm delta CO is proposed.