Small-scale test irradiations of 237Np in the Richland and Savannah River production reactors have provided substantial empirical information on the mechanisms for formation of 236Pu. Application of this information to the design of larger scale irradiations in the Savannah River high flux reactor has resulted in successful production of 2 kg of 238Pu, meeting current isotopic specifications for the heart program. Further work is planned to develop practical technology of producing still larger amounts. The optimum location for target 237Np in the D2O reflector of the high flux charge has been established. Tests have demonstrated that matrix material for the targets is an important variable, and that the use of aluminum should be avoided. Irradiations of kilogram quantities of 241 Am have been completed and most of the resulting 242Cm will be allowed to decay into 238Pu before chemical processing (about two years). However, small amounts of the irradiated 241Am will be processed promptly to provide 242Cm for decay into ultra-high purity 238Pu.