A variety of 6-aryl-4H-s-triazolo[3,4-c]thieno-[2,3-e][1,4]diazepines was synthesized and tested for antipentylenetetrazole activity and inhibition of fighting episodes. The structure-activity relationships are discussed. Some compounds were more active than diazepam in the two assays. Among them, 6-(o-chlorophenyl)-8-ethyl-1-methyl-4H-s-triazolo[3,4-c]thieno[2,3-e][1,4]diazepine was found to have favourable properties as an anxiolytic drug with very low toxicity. Clinical studies of this compound (Y-7131) are under way.