Perlite is a volcanic glass or amorphous aluminium silicate composed of 71-75% SiO2. When heated to 800-1100 degreesC, it expands to form processed perlite, which has a low density, high surface area, and a low thermal conductivity. The objective was to determine the effect of perlite exposure on pulmonary function tests. Pulmonary function tests in conjunction with chest radiogram were carried out in 36 perlite-exposed workers and 22 unexposed office workers in 1992 and 1996. Respirable dust level exceeded permissible dust levels in work places in the 4 years under study. Transfer coefficient (K-CO) decline was significant in nonsmoker perlite-exposed workers (n = 9), and found to be 5.28 +/- 0.71 (predicted 4.32 +/- 0.11) and 3.84 +/- 0.96 (predicted 4.18 +/- 0.18) 1/min/mmHg, in 1992 and 1996, respectively (P < 0.001). Both smoker perlite workers and office workers showed significant obstruction to airflow in small airways with respect to predicted values and 1-year change in transfer factor (T-L, CO) was significant. Although predicted, 12-year perlite exposure did not lead to a decrease in mean pulmonary function test parameters, there was a tendency to a decline in T-L, CO in the 4-year study period, which may be due to high perlite dust levels. As early effects of perlite dust exposure may not be detected by spirometric measurements alone, the transfer coefficient should be added to spirometry. (C) 2001 Academic Press.