A method employing non-radioactive vitamin B(12) and microbiological assay is described for estimating intrinsic factor in gastric juice and for detecting antibody to intrinsic factor in serum. Satisfactory agreement was obtained between the results by this method and by a modification of the method of Ardeman and Chanarin (1963). During the first hour after gastric stimulation 11 patients with pernicious anaemia secreted between 0 and 240 units of intrinsic factor compared with between 1,600 and 39,000 units in 21 patients with other conditions. The results in three out of four patients with gastric atrophy were higher than those in pernicious anaemia but lower than in other conditions.