We introduce and demonstrate a general wave packet method for laser isotope separation. In this scheme, laser excited molecular (or atomic) wave packets of differing isotopes become {ital spatially} separated in the course of their long-time free evolution. In order to overcome the quantum spreading of wave packets, we make use of the phenomenon of revivals. We demonstrate experimentally, with mixed {sup 79}Br{sub 2}/{sup 81}Br{sub 2} isotopes, that significant control over the isotope ratio can be achieved in a single shot. {copyright} {ital 1996 The American Physical Society.}