Results of adhesion tests performed on yttrium (Y), as well as four rare earth metals, samarium (Sm), gadolinium (Gd), dysprosium (Dy), and holmium (Ho), are reported. A modification of the twist-compression bonding method was used to obtain the coefficients of adhesion. Low adhesion values for the above metals were obtained as expected on the basis of the crystal structure considerations. A proposal is made to apply the atomic “size-factor” criterion to the prediction of adhesion properties of dissimilar metals. An illustration of the method is given in terms of adhesion of iron to the above mentioned metals.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Rochester, New York, October 15–17, 1963.