Condensation of aryl hydrazines with ethyl pyruvate gave the respective hydrazones 4-6; Fischer indolization led to substituted-1H-indole-2-carboxylic acid ethyl esters 7-9. The Mannich reaction of these compounds with formaldehyde and morpholine yielded ethyl 3-(morpholinomethyl)-substituted-1H-indole-2-carboxylates 10-12. The 5,7-dichloro-1H-indole-2-carbohydrazide 13 was cyclized with methyl orthoformate in DMF to give 6,8-dichloro[1,2,4]triazino[4,5-a]indol-1(2H)-one 14. Vilsmeier-Haack formylation of 7-9 gave ethyl 3-formyl-substituted-1H-indole-2-carboxylates 15-17 whose 2,2'-((5-chloro-2-(ethoxycarbonyl)-1H-indol-3-yl)methylene)bis-(sulfanediyl) diacetic acid 18 was prepared. The reaction of 15 and 16 with substituted anilines by conventional and microwave methods gave ethyl 3-(N-aryliminomethyl)-5-halo-1H-indole-2-carboxylates 19-29. In a cyclocondensation reaction of 19-25 with thiolactic acid or thioglycolic acid substituted indolylthiazolidinones 30-33 were prepared. Reaction of hydrazine hydrate with 15-17 did not give the respective hydrazones but directly led to the cyclized products substituted-3H-pyridazino[4,5-b]indol-4(5H)-ones 34-36, while a reaction with 2,4-dichlorophenylhydrazine yielded the uncyclized hydrazones. The chlorination of 35 and 36 with POCl3 gave pyridazino[4,5-b]indoles 39 and 40, respectively; reaction of the latter compounds with morpholine gave 4-(substituted-5H-pyridazino[4,5-b]indol-4-yl)morpholine 41 and 42. Mannich reaction of 34 with formaldehyde and N-ethylpiperazine gave 8-chloro-3-((4-ethylpiperazin-1-yl)methyl)-3H-pyridazino[4,5-b]indol-4(5H)-one 43. The microwave assistance of selected reactions has a profound effect on the reaction speed. The structures of the new compounds were confirmed by both analytical and spectral data. Some compounds were subjected to investigations concerning their antimicrobial, tranquilizing, and anticonvulsant activities.