The 1- and 4-hydrazino[1]benzothiéno[2,3-d]pyridazines have been cyclised to form triazolobenzothienopyridazines, tetrazolobenzothienopyridazines and benzothienopyridazinotriazines. NMR study shows a tautomeric equilibrium in solution between tetrazolo [1,5-b][1]benzothiéno[3,2-d] pyridazine and 1- azido [1]benzothieno[2,3-d]pyridazine. Reactions of the benzothienopyridazinotriazones with hydrazine