The synthesis of a number of 5-substituted uracils, eg [E]-5-(2-acylvinyl)uracils 8a-8g is described. These compounds were found to have cytotoxic activities against CCRF-CEM human lymphoblastoid cells, HT-29 colon carcinoma cells and L1210/0 mouse leukemia cells. These compounds were also found to inhibit thymidylate synthase.