Every torsion abelian group has basic subgroups and all its basic subgroups are isomorphic. We extend the concept of basic subgroups from torsion abelian groups to arbitrary abelian groups. The generalized basic subgroups are called mixed basic subgroups. An example of a mixed group is given in which not all mixed basic subgroups are isomorphic. This example also shows that a mixed basic subgroup of a splitting group need not be splitting.