FIELD: analytical methods. SUBSTANCE: invention provides inversion voltammetric method for determining toxic dimethylsulfoxide when analyzing fish-industry reservoir waters and sewages from pulp-and-paper and petrochemical enterprises where permissible dimethylsulfoxide concentration should not exceed 0.01 mg/l and 0.03 mg/l, respectively. To dimethylsulfoxide-containing solution, mercuric chloride is added to concentration 1×10-6-4×10-5 M or mercuric nitrate to concentration 1×10-6-2×10-5 M and electrical thickening is conducted at potential 0.25-0.35 V for 60-120 s followed by recording voltammogram at scanning speed 60-80 mV/s. Content of dimethylsulfoxide is evaluated by standard additive technique wherein, together with standard dimethylsulfoxide solution, 4×10-5 M mercuric chloride or 2-×10-5 mercuric nitrate is added. EFFECT: increased sensitivity and rapidity of analysis. 6 tbl
