The pulmonary surfactant plays an important role in the gas exchange functions of the lungs. Although previous studies suggest that cigarette smoking alters the pulmonary surfactant system in human smokers, the nature of such changes is poorly understood. The aim of the present study was to determine if biochemical and biophysical properties of pulmonary surfactant are affected in rats following chronic exposure to cigarette smoke. Female Sprague-Dawley rats were exposed daily to smoke from the University of Kentucky high tar/high nicotine reference cigarettes, twice a day, for 60 weeks in a nose-only exposure system. Blood carboxyhemoglobin, plasma cotinine, and pulmonary aryl hydrocarbon hydroxylase activity measurements showed that animals effectively inhaled smoke during exposures. At termination, the bronchoalveolar lavage fluids (BALF) and the lung tissues were collected for biochemical and biophysical analyses of surfactant. The total phospholipid content of the BALF and the lung tissues from room control (RC), sham-treated (SH), and smoke-exposed (SM) animals were the same among the different groups. However, disaturated phosphatidylcholine (DSPC) levels in the BALF were significantly decreased in SM rats compared to RC or SH groups. In contrast, the lung tissue DSPC content in SM rats was not significantly different from that of control groups. Phospholipid profile analysis of the BALF also did not reveal any significant differences among other major constituents of surfactant from control and SM animals. The organic extracts of BALF obtained from different animal groups were assessed for surface activity using a Wilhelmy balance. The results showed an increase in surface compressibility and a reduction in respreadability index in SM group.(ABSTRACT TRUNCATED AT 250 WORDS)