The apolipoprotein E (APOE) epsilon4 allele is associated with late-onset Alzheimer's disease and cognitive function in aging normal populations. To study the effect of the presence of the epsilon4 allele on cognitive function, we compared intelligence-test scores and component values for event-related potentials for epsilon4 and non-epsilon4 carriers in a group of 134 young females. The results demonstrate modest increases in performance intelligence quotient (IQ) and N100 amplitude for epsilon4 carriers (P=0.038 and 0.068, respectively). Our findings suggest that cognitive impairment, associated with the presence of the epsilon4 allele, is age-dependent and thus not probable for young women. The higher performance IQ scores demonstrated for epsilon4 carriers require further exploration.