Data on 1133 men and 1621 women who smoke solely cigarettes with a known tar yield are extracted from the baseline population survey of the Scottish Heart Health Study. The expired-air carbon monoxide (CO-E), serum thiocyanate and serum cotinine values are compared between smokers in three tar groups: low (below 13 mg/cig.), middle (14-15 mg/cig.) and high tar (above 15 mg/cig.). An index of tar consumption is calculated assuming that the intake of different smoke components relative to one another is in proportion to their concentration in the smoke. CO-E and cotinine are found to peak in the middle tar group. Thiocyanate only tends to increase from low to middle tar group for women and from middle to high tar group for men. Tar consumption increases with tar yield of the cigarette smoked, but the increase is much lower than would be expected. We conclude that the tar yield of a cigarette is not an accurate guide to the amount of smoke components consumed by its smoker. Health professionals should be aware of these limitations of tar yield as a measure of cigarette strength.