A simple model of a metal containing deuterons is considered. The example of palladium is treated in detail. It is shown that the effect of screening of Coulomb fields by conduction electrons is sufficient to allow deuteron pairs to fuse at rates of 10(-30) sec(-1), seven orders of magnitude smaller than those reported by Jones et al. [Jones, S. E., Palmer, E. P., Czirr, J. B., Decker, D. L., Jensen, G. L., Thorne, J. M., Taylor, S. F. & Rafelski, J. (1989) Nature (London) 388, 737-740].