A new generator system has been developed using the Fe-52 leads to Mn-52m parent-daughter pair. Fe-52, half-life 8.3 hr, is isolated on an anion-exchange column, and Mn-52m is eluted in hydrochloric acid. Breakthrough is less than 0.01% and the yield is 75%. The 21.1-min half life of Mn-52m is ideal for use in sequential studies, but is long enough to permit radiochemical manipulations to control biodistribution. Animal studies indicate that Mn-52m is an ideal nuclide for myocardial imaging, combining rapid blood clearance and high concentration in the myocardium. An added advantage is that Mn-52m decays 98% by positron emission and is useful for positron computer tomography.