Current studies indicated that emphysema in smokers might be due, in part, to the local suppression of G, -protease inhibitor(u, -Pl) in lung by reactive oxygen species in cigarette smoke or smoke-activated lung neutrophiles. In the present works, we examined the possibility that a measure which inactivated $alpha$l-Pl by cigarette smoke could be an alternative method to evaluate the cigarette quality, In order to determine the inactivation of $alpha$1, -Pl, trypsin inhibitory capacity(TIC) was assayed. A rapid loss of $alpha$1, -Pl activity occurred when $alpha$1-Pl solutions was exposed the gas phase or total particulate matter(TPM) obtained from various brands. The inactivation of $alpha$1-Pl by gas phase was dependent upon the number of puffs and the age of the smoke. However, that by TPM was rather decreased since 2 puffs and also showed no more change over 24hrs after exposing. Inactivation of $alpha$1-Pl determined by our suggested method(5 puffs, 24hours of aging after exposing) using various commercial cigarettes exhibited that high tar brands has inactivated it more strongly than low tar cigarettes. But the ability of some brands to inactivate $alpha$1-Pl does not correlate with the content of tar or nicotine. These results so여esc that the degree of $alpha$1-Pl inactivation by cigarette smoke may be a useful index for the evaluation of cigarette quality and that it should be also contribute to the manufacture of less hazardous cigarettes.