New data on the evolution of Muroidea necessitate taxonomical changes, particularly the erection of new families and subfamilies. [The Cricetidae, Nesomyidae, Rhizomyidae, Gerbillidae, Arvicolidae, DENDROMURIDAE fam. nov. (including Dendromarinae Allen, 1939 and Petromyscinae Roberts, 1958), CRICETOMYIDAE fam. nov. (includes the Cricetomyinae) and Muridae are dealt with.].