In this study, a new class of 4-amino-3-substituted-1,2,4-triazole-5-thiones (1-4) and their corresponding condensed derivatives 3,6-disubstituted 7H-1,2,4-triazolo[3,4-bi-1,3,4-thiadiazines (1a-4c) were synthesized and evaluated for their analgesic/anti-inflammatory activities. All synthesized compounds were also tested for their gastric toxicity and antioxidant activity on acute administration. Most of the compounds showed significant activity in both carrageenan-induced oedema and acetic acid-induced writhing tests besides negligible gastrointestinal toxicity. The compounds showing less ulcerogenic effect also showed less lipid peroxidation (LPO) level. Most promising results were obtained with the compounds that placed a fluoro or a chloride on the phenyl ring at the sixth position of the fused ring. (C) 2009 Elsevier Masson SAS. All rights reserved.