The free radical scavenging effect of the hydrochloride of (+/-)-trans-2-(1-pyrrolidinyl-)cyclohexylester of 3-(n)-pentyloxy carbanilic acid, pentacaine (trapencaine I.N.N), and its derivatives and other substances, lidocaine, stobadine, mannitol, and ascorbic acid was tested in the presence of diphenyl-p-picrylhydrazyl (decrease in absorbance). In this method, more pronounced antiradical activity was observed with trapencaine, more effective than stobadine, ascorbate, and mannitol. Trapencaine derivatives and lidocaine were less effective in comparison with trapencaine. After introducing a methylene group into the hydrophilic moiety of the trapencaine molecule (stereoisomers P-18, P-20), there was a loss of antiradical activity, but the cis-isomer is more effective than the transisomer. The results demonstrate the existence of relationships between the chemical structure, antiradical and gastric-cytoprotective activity.