The average shearing strength of surgical Simplex P bone cement has been experimentally evaluated and found to be 5,762 plus or minus 180 psi. The average shearing strength for compact bone is about 10,000 psi. Therefore surgical Simplex P does not resist shear forces as well as compact bone and should not be used as a substitute for bone whenever possible. The inclusion of 10 per cent barium sulfate U.S.P. for radiographic purposes does not adversely affect the shear strength of the cement. This amount of barium is the same percentage by weight as that found in radiopaque Simplex P in clinical usage today. Varying the loading rate between 0.005 and 0.5 in/min slightly affected the magnitude of the shear force at failure. A comparison of the effect of short term curing times on the magnitude of the shear force at failure reveals that surgical Simplex P strengthens with time. The curing periods varied from 2 to 168 hours.