The original work consists of two projects: In the first project: 5-(Aryldiazenyl)-thiazoles and 1,3,4-thiadiazoles bearing indole were synthesized via reaction of hydrazonoyl halides and indole-thiosemicarbazone and alkyl (indolyl)carbodithioate, respectively. In the second project: 3-Acetylindole proved to be a useful precursor for the synthesis of various 1,3-thiazoles, 1,3,4-thiadiazoles and pyrido[3,2-e][1,2,4] triazolo[4,3-a]pyrimidin-5(7H)-one. Fifteen of the new compounds have been evaluated for their antitumor activity against the human breast carcinoma cell line. The results indicated that many of the tested compounds showed moderate to high anticancer activity.