Effects of mechanical compression of the filter tips and of blocking the air channels of a special filter design on the smoke yields of seven brands of commercial filter cigarettes were investigated. In addition, the influence of these variables on actual uptake of smoke constituents by smokers was studied with four subjects. Compression of filter tips produced major increases in smoke yields for the cigarette which features a filter tip with four longitudinal air channels at its periphery. Blocking of these air channels increased tar yields by 51 per cent, nicotine by 69 per cent, and carbon monoxide by 147 per cent. Subjects who smoked the cigarette with this special filter design tended to smoke fewer cigarettes per day than when they smoked cigarettes with perforated filter tips, yet their plasma cotinine levels were significantly higher. Blood pressure and pulse rate were markedly elevated after first exposure to smoke from the special filter cigarette, as were plasma nicotine levels. These results point out that individuals inhale different quantities of smoke constituents from cigarettes with reportedly similar smoke yields according to Federal Trade Commission methods. A redefinition of "average" smoking parameters readjustment of standard laboratory methodology are suggested.