Each of four composite samples of one day's whole meals were homogenized and digested with pepsin followed by pancreatin. Approximately 40-80% of the total manganese in the diets was extracted into the soluble fraction at pH 1.5 both with and without pepsin. The solubility of the manganese in the diets was not increased by pepsin digestion. The solubility of the manganese components in the diets was reduced to less than 30% by adjustment of the pH from 1.5 to 8. Little increase in the solubility of the manganese components was observed after pancreatic digestion for 1h. The low absorption of manganese from food may therefore depend partly on the low solubility of manganese in the area of the duodenum. Gel chromatography of the soluble fraction after in vitro digestion revealed several kinds of soluble manganese components over a wide molecular weight range. Therefore, for further investigation of the mechanism of manganese absorption in man, it will be necessary to isolate each manganese component in the digest.