To assess clinical effects of precipitated amorphous silica (PAS), we have reviewed serial spirograms, respiratory questionnaires, and chest radiographs of 165 workers exposed for a mean of 8.6 years. Monthly exposure was graded on a 1 to 4 scale and a cumulative exposure index (CEI) calculated for each worker from the sum of measured exposure. A mean exposure index was calculated by dividing the CEI by total months exposed. Sputum production and dyspnea were inversely correlated with CEI, while cough and dyspnea correlated with mean pack years of smoking but not PAS exposure. Linear regression analysis of yearly change of all pulmonary function variables (FVC, FEV₁, FEV₁/FVC, FEF25-75) showed no correlation with either the dose of PAS (CEI) or total years of exposure. Among 44 workers with a mean exposure time of 18 years (range 10 to 35 years), the yearly decline of FVC and FEV₁ were similar to the overall group. Of 143 workers with serial radiographs and exposure to only PAS, none had radiographic pneumoconiosis. Respiratory symptoms in PAS workers correlated with smoking but not with PAS exposure, while serial pulmonary function values and chest radiographs are not adversely affected by long-term exposure.