The present experiments explore the generality of some recent findings relating IQ to a measure known as Inspection Time (IT) - the exposure duration necessary to judge which of two briefly presented straight lines is the longer. In the first study IT and verbal and performance IQ scores were obtained from a large group of normal six- and seven-year-old children. In contrast to some previous suggestions verbal IQ and full-scale IQ did not correlate significantly with IT, and performance IQ showed only a weak correlation with IT (r = −0.29). In the second experiment IT was found to correlate much more highly with performance IQ in a sample of mentally retarded subjects (r = −0.71). Some possible implications of these results for theories of intelligence and of mental retardation are discussed.