In order to determine the acute effect of smoking on elastase in bronchoalveolar lavage fluid (BAL), we obtained BAL from 30 smokers twice, the first before smoking (after 8 h of abstinence) and the second 2 min to 1 h after the subjects had smoked either 2 or 4 cigarettes. Bronchoalveolar lavage was concentrated 100-fold and was assayed for elastaselike activity against succinyl-trialanyl-p-nitroanilide (SLAPN) as substrate. Elastolytic activity against insoluble 3H-elastin and immunologic neutrophil elastase levels tested with a sensitive enzyme-linked immunosorbent assay were determined in some subjects. No activity against insoluble 3H-elastin was detected using a sensitive assay capable of detecting subnanogram quantities of elastase. Total elastaselike activity in BAL against SLAPN was significantly (p less than 0.02) increased in smokers prior to smoking (47.4 +/- SD 20.2 ng human neutrophil elastase (HNE) equivalents) when compared with BAL from 7 nonsmokers (26.3 +/- SD 13.4 ng HNE); however, there was no significant change in enzyme activity in smokers' BAL after smoking. Assays with EDTA and phenyl-methyl-sulfonyl-fluoride as inhibitors suggested that approximately two thirds of elastaselike activity was due to a metalloprotease and that there was negligible serine protease activity.(ABSTRACT TRUNCATED AT 250 WORDS)