Evidence of a relationship between the electrical responses of the human brain and psychometric measure of intelligence is presented. These involuntary cortical responses, known as average evoked potentials are considered to be the electrical signs of information processing by the brain. The time delays of these responses from presentation of a light flash show highly significant inverse correlations with IQ scores on three common psychometric tests of intelligence in a random sample of 573 primary school pupils. Evidence is offered in support of a concept of "neural efficiency" as the biological substrate of individual differences in behavioral intelligence. Results could be useful in the development of a culture and language free measurement of intellectual potential. (Author)