5-Hydroxymethyldeoxyuridine is a nucleoside analog with potent anticancer and antiviral activities. It inhibits the replication of murine S180 lung carcinoma cells and Ehrlich ascites mammary carcinoma cells (ED50s = 8.5 and 4 μM, respectively) and multiple human leukemia cell lines (IC50s = 1.7-5.8 μM).