Comparison of the effectiveness of antioxidant activity of three thiol compounds, D-penicillamine, reduced L-glutathione, and 1,4-dithioerythritol, expressed as a radical-scavenging capacity based on the two independent methods, namely a decolorization 2,2'-azinobis[3-ethylbenzothiazoline-6-sulfonic acid] assay and a rotational viscometry, is reported. Particular concern was focused on the testing of potential free-radical scavenging effects of thiols against hyaluronan degradation, induced by hydroxyl radicals. A promising, solvent-independent, antioxidative function of 1,4-dithioerythritol, comparable to that of a standard compound, Trolox(®), was confirmed by the 2,2'-azinobis[3-ethylbenzothiazoline-6-sulfonic acid] assay. The new potential antioxidant 1,4-dithioerythritol exhibited very good solubility in a variety of solvents (e.g., H(2)O, EtOH, and DMSO) and could be widely accepted and used as an effective antioxidant standard instead of a routinely used Trolox(®) on 2,2'-azinobis[3-ethylbenzothiazoline-6-sulfonic acid] assay.