The physics parameters of a bare sphere of metallic 237Np have been investigated. The calculations indicate that a chain reaction can be sustained with fast neutrons. The predicted critical radius is 8.86 cm, and the corresponding critical mass is 59.7 kg. Kinetic parameters such as the prompt neutron lifetime, l, the prompt neutron decay constant at delayed criticality, αc, and the effective delayed neutron fraction, βeff, were also calculated. With respect to the last quantity, the phenomenon of the so-called “vanishing dollar” in systems consisting of even-neutron nuclei is discussed. Some remarks concerning the possible utilization of 237Np, which is produced in nuclear power reactors as a by-product, are appended.