The conductances of a number of tetra-n-alkylammonium bromides and iodides have been measured in acetonitrile. Limiting equivalent conductances and dissociation constants have been evaluated by two methods. Limiting equivalent ionic conductances have been evaluated from these results. Correlations have been made of the effect of ion size on the ionic conductances and on the relative order of magnitude of the dissociation constants. In an appendix the limiting ionic conductances of a number of other ions have been collected from the existing literature.