Many of the proteins that are members of the kinesin family of microtubule motor proteins are plus-end motors; however, a few of the kinesin proteins have now been found to be minus-end microtubule motors. Overall structural features of the proteins can be used to identify further kinesins that are likely to be minus-end motors. Structural or biochemical differences that may serve as the basis of the 'reversed' polarity of a unique subset of the kinesin proteins are discussed.