This paper deals primarily with the fatigue of shafts with press-fitted members, a problem frequently arising in connection with rotating machinery involving gears, wheels, couplings, rotors, etc. Failures at the edge of fitted members are not uncommon in practice. A survey is made of existing data, after which a report of fatigue tests on the press-fit problem carried out at the Westinghouse Research Laboratories is given. A related photo-elastic investigation and stress analysis is also reported. Practical expedients for increasing the strength of shafts with fitted members are given. Suggestions for future research along the foregoing lines are made throughout the paper.