In this study, some novel 2,6-dimethyl-N'-substituted phenylmethylene-imidazo[2,1-b][1,3,4]thiadiazole-5-carbohydrazides (3a-3h) were synthesized from 2,6-dimethylimidazo-[2,1-b][1,3,4]thiadiazole-5-carbohydrazide (2). The newly synthesized compounds (3a-3h) were evaluated in the National Cancer Institute's 3-cell line, one dose in vitro primary cytotoxicity assay. Compounds 3c and 3h which passed the criteria for activity in this assay (20-29% growth percentages) were scheduled automatically for evaluation against the full panel of 60 human tumor cell lines at a minimum of five concentrations at 10-fold dilutions. Sulforhodamine B (SRB) protein assay was used to estimate cell stability or growth. 2,6-Dimethyl-N'-(2-hydroxyphenylmethylidene)imidazo[2,1b][1,3,4]thiadiazole-5-carbohydrazide (3c) showed the most favorable cytotoxicity. This compound demonstrated the most marked effects in the National Cancer Institute's 60 human tumor cell line in vitro screen on an ovarian cancer cell line (OVCAR log(10) GI(50) value -5.51). (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.