In urine the level of thiodiglycolic acid (TDGA) is a sensitive indicator of exposure of the human organism to some physiologically active or toxic substances, gases and vapors. The determination of TDGA by use of a voltammetric method based on electroreduction of TDGA in acidic solution at the hanging mercury drop electrode has been developed and practically tested. In order to eliminate the matrix effect of urine, prior to voltammetric measurement the samples are eluted from a small column of PVC powder. The method is simple, low cost, rapid and sensitive, appropriate for the needs of occupational medicine.