In work on the reserve foods of the bracken fern, a more accurate method of estimating starch in small quantities was required than those which involve comparison of determinations of the sugar mixture, obtained after hydrolysis, by reduction of Cu salts, and by the polarimeter, as the quantities were too small for use of the polarimeter. A method was therefore devised by which the Cu-reduc-ing power of the hydrolysed starch was related to the reducing power of known quantities of a carefully purified starch preparation. Such a method does not give absolute values as the reducing power of starches of different origins is not the same. It does, however, give values comparable with each other for any 1 material and this is sufficient for many purposes, such as the comparison of the amounts of starch present at different stages of development.