Observations of spin-flopping, or decoupling between the direction of antiferromagnetism and the easyaxis of the crystal, are presented forMnF2in single crystal and powder form at low temperatures. Magnetizationmeasurements in pulsed fields to 140 koe are employed to explore the critical interaction energy inthis antiferromagnet, as an alternative tool to microwave resonance. The orientation dependence predictedby Ne´el in 1936 is confirmed. The critical field for spin-flopping given by the combination of anisotropy andexchange,(2HEHA)12is found to be 93±2 koe in excellent agreement with resonance results of S. Foner[(a) Phys. Rev.107, 683 (1957); (b) J. phys. radium20, 336 (1959)], and F. M. Johnson and A. H.Nethercot [Phys. Rev.104, 847 (1956);114, 705 (1959)].