The existing ANSI standard for determining residual thiosulfate (hypo) in processed films and papers is not valid for certain kinds of photographic papers. The ANSI standard consists of two methods, the methylene blue method and the densitometric method. A colorimetric method for determining residual hypo in films, published in 1966, proved effective for paper samples that could not be measured by the methylene blue method. The colorimetric method consists of eluting thiosulfate from a paper sample, and then adding the eluent to an iodine-amylose solution. The loss of iodine-amylose color is a measure of the residual thiosulfate removed from the paper into the eluent.