2-Thio-6-phenyl-thiazolino(4,5-d)-pyridazin-7-one (IV) and 2,3-dihydro-6-phenyl-p-dithiino-(2,3-d)-pyridazin-5(6H)-one (VIII) and somederivatives have been prepared from 1-phenyl-4,5-dibromo-6(1H)-pyridazinone (I). Treatment of I with ammonia yielded the monoamino compound (II) and with ethanolic KHS solution the corresponding dimercapto compound (V) was obtained.