Excitation functions for the (p, pn) reaction have been determined in the energy range 250 Mev to 440 Mev for the target nuclei As75, Br81, Zr96, I127, Ce142, W186, and Re187. Both isomer products were determined in the case of the Br81(p, pn)Br80 reaction. Also, excitation functions were determined for the (p, 2p) reaction on Zr96, Ce142, and W186 and for the (p, 2n) reaction on Zr96. All cross sections were measured relative to the Al27(p, 3pn)Na24 excitation function. The (p, pn) excitation functions are only moderately sensitive to energy showing an increase by about 30% for iodine, 20% for arsenic and cerium, and a 12% decrease for zirconium. The remaining excitation functions are flat. The ratio of σp,pn to σp,2p is 1.62+/-0.09, for the three targets measured, at 440 Mev. The various mechanisms for the production of reactions of this type are examined in the light of present understanding. The suggestion is made that, despite the relative insensitiveness of these excitation functions to energy, (p, pn) and (p, 2p) reactions may take place by more than one mechanism in this energy region. A comparison is made with the results of recent Monte Carlo nuclear cascade calculations applied to calculation of (p, pn) reaction excitation functions.