Dynamic polarizabilities of halide and H- ions are computed by applying dispersion relations to photodetachment cross sections. Recent calculations of photodetachment cross sections using the relativistic random-phase approximation were used for the halides F-, Cl-, Br-, and I-. The bound-state to free-state absorption coefficient of H- evaluated previously using a set of successively improved bound- and free-state wave functions was used to obtain the polarizability of H-. The H- result is compared with other recent theoretical calculations. Results for the static polarizabilities ±(=0) are compared with other theoretical techniques and experiment. © 1992 The American Physical Society.