The aim of this study was to obtain some evidence of a protective role for pulmonary surfactant in the pathogenesis of emphysema. Firstly, we developed a quick and easy method to treat mice with a series of intratracheal instillations. Subsequently, three groups of mice were treated as follows: two groups received intratracheal instillations with pancreatic elastase (1.8 mg.kg-1 BW) followed after 3, 48 and 96 h in one group (El/Surf group) by intratracheal administration of surfactant (100 mg phospholipid.kg-1 BW), and in the other group by instillations with saline (El/s group). The third group of control mice was treated with saline followed by three doses of surfactant (s/Surf group). After eight weeks, the mice were killed and emphysema was measured by calculating the mean linear intercepts (Lm) of airspaces. The Lm values in the different groups were statistically tested for differences by the Mann-Whitney test. Instillation of pancreatic elastase (El/s group) resulted in an evenly distributed increase in Lm compared with the control group. Administration of surfactant in elastase-treated mice (El/Surf group) resulted in a statistically significant inhibition of airspace enlargement. Although the Lm in the El/Surf group was still higher than in the control group, analysis of histograms of Lm values per field of examination revealed that the Lm distribution in the former group was similar to that of the s/Surf group. The El/s group, on the contrary, showed the presence of many fields with enlarged air spaces. Repeated instillations with saline and/or surfactant had no effect on the Lm.(ABSTRACT TRUNCATED AT 250 WORDS)