The effects of asbestos-induced benign pleural conditions on pulmonary function have been controversial since this subject was first studied in the mid-1960s. Firm conclusions have been difficult to reach because of (1) the difficulty of taking into account asbestos exposure, which may have effects on pulmonary function other than those mediated through pleural lesions, (2) the disagreement over the type and extent of radiographic pleural abnormalities, (3) the imprecision in measuring pulmonary function, and (4) the numerous potential confounding factors of reduced pulmonary function, such as cigarette smoking, age, concurrent occupational exposures, and prior chest diseases or trauma. This article critically evaluates the published reports on the functional significance of asbestos-induced pleural conditions. The results of this analysis lead to the conclusion that (1) pleural plaques are not associated with clinically significant reductions in pulmonary function, (2) diffuse pleural thickening, when extensive, can severely impair ventilation, and (3) restriction with a preserved diffusing capacity is the expected pattern when pleural lesions are responsible for reduced pulmonary function.