1. An in vitro cellular model of injury was used to elucidate mechanisms contributing to traumatic brain injury (TBI). Neonatal rat cortical neurons cultured on a flexible silastic membrane were stretched rapidly and reversibly by a 50-ms pulse of pressurized air. 2. Sublethal cell stretch depolarized neuronal resting membrane potential by approximately 10 mV but only if cells were incubated for 1 h after injury. Stretch-induced delayed depolarization (or SIDD) returned to baseline values within 24 h. 3. SIDD was dependent on the degree of cell stretch and required neuronal firing, calcium entry, and N-methyl-D-aspartate receptor activation for its induction but not its maintainance. 4. Similarities between SIDD and TBI suggest that SIDD may play a role in brain injury.