The influence of shocks on the abundances of molecules in diffuse interstellar clouds is investigated with special emphasis on molecular CH/sup +/. Idealized shocks with plausible parameters are found to produce column densities for CH/sup +/ in the hot, postshock gas which are comparable with measured values in interstellar clouds (up to about 10/sup 13/ cm/sup -2/). Abundances of other molecules which are generated by these shocks are within acceptable observational limits. Abundances of interstellar CH/sup +/ apparently cannot be understood, except perhaps in special cases, in terms of other proposed processes. The cause of the shock probably varies from cloud to cloud. Shocks in diffuse interstellar clouds are difficult to detect directly, and have not been observed by other means. The further study presented here is motivated in part by two developments which are encouraging for the shock interpretation of CH/sup +/ abundances. A key uncertainty in the previous work: the cross sections for rotational excitation of H/sub 2/ by H atoms: has received further study in extensive calculations by Green and Truhlar. An observational study has delineated the ''preshock'' gas in the direction of zeta Ophiuchi through OH radio emission.