[en] The 41-cm double-focusing mass spectrometer at the University of Minnesota has been used to measure the atomic masses of ¹⁵²Sm and ¹⁵⁴Sm and the isotopic mass differences of most Sm and Gd isotopes. Through the use of a new generalized error signal technique, measurements on the narrow doublets of Sm and Gd chlorides gave improved mass differences over previous work in this mass region. Where intense peaks were available, the results are consistent with errors of 0.4 to 1.0 μu. The conventional wide doublet technique was used to measured Sm-hydrocarbon doublets, yielding the masses of ¹⁵²Sm and ¹⁵⁴Sm with errors of less than 4 μu. These new mass data, when combined with other mass measurements and reaction data of comparable accuracy, are used in a least-squares mass adjustment in the range of 141 to 160 u