The dependency of fracture on the rate of strain of a range of polyethylene samples was measured in three point flexural tests at 23°C. The range of strain rates from 10−1 to 10−7 reciprocal seconds was examined. The J integrals at the initiation of the cracks were determined. This enabled the interrelationship between fracture initiation and the test rate to be established. The dependency follows a power law relation. The values of the exponents in the power law equations, derived from experiment, were found to be higher than the values calculated using established criteria for crack initiation. The difference is postulated to be due to the strengthening of the fibrils ahead of the crack because of the orientation of the fibrils in that region.