This paper reports the follwing facts as revealed by a dust investigation of the working environment and by medical examinations of workers working in the same environment in two activated-carbon manufactories, in Kanagawa Prefecture, in 1962. (1) Concentrations of dust in air exceeded the maximum allowable concentration, ranging from 3 up to 96 mg/m3. Size of dust in air was distributed between 0.1μ (minimum) and 7.0μ (maximum). 92.4% of the dust was under 1μ. (2) Radiographical examination revealed that out of thirty six workers, who had been exposed to a considerable quantity of the dust more than one year, five were found to be in Category 1 and six were in Category 2, according to the International Classification of Radiograph on Pneumoconiosis. Smaller opacities shown under radiograph were all of the "punctiform" type. Generally speaking, the more the years of employment of the worker in dusty environments, the more was the number of cases of pneumoconiosis. (3) Authors supposed that pneumoconiosis could be caused by carbon dust from charcoal.