The yields of 40 toxic smoke constituents per mg nicotine were computed in three matched pairs of higher- and lower-tar cigarettes tested in the 1999 Massachusetts Benchmark Study. In the three pairs, 19, 20 and 17 compounds, respectively, exhibited significantly greater yields per mg nicotine in the lower-tar than the corresponding higher-tar brand. Based on the assumption that toxicant yields per mg nicotine were independent of smoking intensity, the minimum degree of nicotine compensation necessary to obtain equal or greater dosages of these toxic compounds from the lower-tar cigarette ranged from 0% to 73%. A smoker who compensates only incompletely for nicotine may thus obtain a higher dosage of a specific smoke toxicant from a lower-tar cigarette than from a higher-tar cigarette. From the toxicological standpoint, incomplete compensation for nicotine does not necessarily translate into harm reduction.