Investigations into protein folding have concentrated on experimentally tractable proteins with the result that membrane protein folding remains unsolved. New evidence is providing insight into the nature of the interactions stabilising the folded state of alpha-helical membrane proteins as well as giving hints on the character of the folding transition state. These developments show that classical methods used for water-soluble proteins can be successfully adapted for membrane proteins. The advances, coupled with increasing numbers of solved crystal structures, augur well for future research into the mechanisms of membrane protein folding.