The report presents the clinical and environmental findings of a cooperative investigation into the exposures of ferrous foundry workers to silicosis and other hazards. Environmental investigations were made in 18 ferrous foundries, in which approximately 1,100 samples of air-borne dust were collected and studied. The amount of free silica in the air-borne dust varied with the operation and ranged from 13 percent at coremaking to 29 percent in pouring, shakeout and sand conditioning. The percentage of iron in the air-borne dust was found to range from 3 to 9 percent for all operations except casting cleaning, for which the proportion varied from 30 to 38 percent. Operational dust levels at various foundry activities in general were found to be much lower than those reported in earlier investigations. Concentrations of aldehydes were of a low order of magnitude. Carbon monoxide concentrations were relatively low in most instances. The most significant clinical findings dealt with those of the respiratory system. Pulmonary fibrosis of occupational origin was found in 9.2 percent of the men. Reinfection type of tuberculosis was found in 0.7 percent of white workers and in 1.7 percent of the Negroes. Skin diseases probably of occupational origin, was found in 1.7 percent of the men. The correlation of the clinical and environmental findings reveals that there is no reason to believe that dust conditions in the foundries studied have improved in the past 10 to 20 years.