The general knowledge of rock permeability has been reviewed in the light of fundamental work done since Rove's pioneer study, and an attempt has been made to evaluate the influence of permeability on ore distribution in limestone and dolomite. Over 1,000 permeability determinations were made, principally on rocks from the East Tennessee Zinc District. A permeameter is described which was especially designed to measure permeabilities in the range 10 (super -2) to 10 (super -7) millidarcies, using either liquid or gas as the test fluid. The potential sources of error in using gas-flow results to predict liquid flow through rocks are discussed with particular note being given to Klinkenberg's discovery that only at infinite mean gas pressure will "gas permeability" approximate "liquid permeability."In the East Tennessee Zinc District the permeability values fall into three main groups corresponding to the three principal rock types: "original" dolomites, limestone, and "recrystalline," the latter an alteration product of the limestone near mineralization. Alteration of certain beds by the mineralizing solutions prior to sulphide introduction increased their permeability many fold; disseminated replacement ore is virtually restricted to these beds. Calculations from test results show that, under reasonable geologic conditions, large volumes of aqueous solutions can pass through rocks of the "recrystalline" type. In all probability a sufficient volume of dilute ore solution could pass through these rocks to account for all the ore deposits found in them.