FIELD: organic chemistry, heterocyclic compounds, medicine, oncology. SUBSTANCE: invention relates to novel crystalline modification of 5-fluoro-1-(tetrahydro-2-furyl)-uracil and also to complex compounds of this form with 2,4-dioxo-6-methyl-1,2,3,4-tetrahydropyrimidine or licorice roots extract (Radices Glycyrrhizae). By its indices this form differs from the early known modification of this compound and shows the enhanced antitumor activity and used in medicine. New form shows the enhanced stability and it can form stable molecular complexes with biologically active compounds that elicit similar properties. EFFECT: enhanced activity and stability of synthesized compounds. 10 cl, 14 dwg, 2 tbl, 4 ex
