Columbia University microbeam was constructed in 1993 andfinished by the end of 1995. It is well established and used routinely toirradiate cells in a highly localized spatial region with a defined number ofα-particles. By using this probe, it is possible to study a number ofradiobiological questions in ways that cannot be simulated by usingconventional broad-field exposures. This report describes the developmentand current capabilities of the Columbia University microbeam, as well as thepreliminary researches undertaken.