The methods for the purification of functionally active mitochondrial porin or voltage-dependent anion channel of the outer mitochondrial membrane are critically evaluated. Two rapid and efficient methods are now available. Both make use of a hydroxyapatite/celite column as a single chromatographic step. However, in one method with long polar head-group detergents, porin passes through the column, whereas in the other method, with shorter polar head-group detergents, porin is first bound to the column and then eluted by the addition of salts. On the basis of these results, a model for the arrangement of porin in the detergent-protein micelles is proposed.