A simple method is reported for standardizing 10-5-10-4 M dithizone solutions for titrimetric analysis. Dithizone in an anhydrous acetic acid/chloroform (4% v/v) medium is titrated with 2 × 10-4 M mercury(II) acetate in the same medium. The titratioin takes only a few minutes. The accuracy (+0.2%) and precision (r.s.d. = 0.7%) achieved are similar to those obtained by the classical extractive titration with silver(I). © 1985.