In 1888, Hutchinson1 ascribed arsenic as the cause of epitheliomas and keratoses occurring in patients with a history of ingestion of potassium arsenite solution (Fowler's solution) for medicinal purposes. Since then, sufficient quantitative data has not been available to evaluate the etiologic significance of the actual amount of arsenic contained, not only in the arsenical epitheliomas, but also in keratoses and normal skin. This study was undertaken to determine the amount of arsenic found in normal skin, epitheliomas, and keratoses in patients with a history of arsenic ingestion and to compare these amounts with those found in normal skin, epitheliomas, and keratoses occurring in patients with no arsenic history. With the results of these findings it was anticipated that there would be further elucidation as to whether there is an increased amount of arsenic in arsenical epitheliomas in comparison to that of the adjacent