High-energy neutron cross sections for 237Np are needed to calculate unwanted 236Pu contaminant in 238Pu product made for heat source applications in space and medical projects. Recent improved determination of 236Pu formation by 237Np(n, 2n) reactions completes the information needed to calculate 236Pu/238Pu ratios over a wide range of 237Np irradiation environments, from D2O reflectors to pressurized-water-reactor fuel. The 237Np(n, 2n) 236&Np cross section is 63 ± 6 mb, averaged over the 235U fission spectrum >6.8 MeV; this result is consistent with the cross section calculated by Pearlstein.