The authors describe a manual method for the direct assay of iron in human serum using the ammonium salt of Chromazurol B. This new chromogen reacts with ferric or ferrous ions and cetyltrimethylammonium bromide giving a purple ternary complex. Reliability and practicability of the method are studied. The results correlate very well either with those of the SFBC's method or with a direct ferrozine-guanidine kit. The reagents are very cheap, the method is quickly performed; no significant interference could be observed in case of high concentrations of added bilirubin, copper or hemoglobin.