The present study examines long-term effects of occupational exposure to formaldehyde fumes on lung function. Forced spirometry and diffusing lung capacity were measured in 16 health-service professionals (8 medical doctors and 8 laboratory technicians) working at the pathoanatomic laboratory for at least 4 years with daily exposure 8 +/- 1 hours. Control group employed 16 males, which were matched by age and stature to members of the exposed group. Only non-smokers were included in the study. Spirometric parameters in study participants exposed to formaldehyde fumes compared to control group were not significantly different indicating absence of restrictive and/or obstructive deterioration of lung function in exposed group. The only parameter differing in two groups was blood volume of pulmonary capillaries (Vc') which was significantly larger in a group exposed to formaldehyde fumes. The possibility that the hyperemic lung reaction is the consequence of the exposure to formaldehyde fumes should be further explored.