Measurements have been made with strain gauges of the magnetostriction and thermal expansion of single crystals of gadolinium. The four magnetostriction constants of a hexagonal crystal have been determined from 4°K to above the Curie point, using fields to 30 kOe. The maximum in the forced magnetostriction, near the Curie point, is large and positive when the strain is measured parallel to the c axis, and small and negative perpendicular to this axis. Related to the forced magnetostriction is the anomaly in the thermal expansion coefficient; this shows a sharp maximum when the coefficient is measured parallel to a (as in nickel) and a minimum when measured parallel to c (as in iron), corresponding to positions, respectively, to the right and left of the maximum of the Bethe-Slater curve. © 1963 The American Institute of Physics.