On the basis of intelligence test performance, Dershowitz and Frankel have hypothesized that Jewish subjects are less psychologically differentiated (more field dependent) than Protestant and Catholic subjects. It is argued that differential intelligence test patterns are better explained in terms of differential emphasis on abilities mediated by the left and right cerebral hemispheres. The hypothesis is advanced that Jewish subjects exhibit a tendency toward lefthemisphere dominance in comparison to Protestant and Catholic subjects. Evidence for, and implications of, the hypothesis are discussed. Dershowitz and Frankel (1975) have recently summarized the results of a number of studies showing that Jewish subjects tend to be characterized by relatively low scores on some of the performance subtests of the Wechsler Intelligence Scale for Children (WISC) and of the Wechsler Adult Intelligence Scale. Scores on Picture Completion, Picture Arrangement, Block Design, and Object Assembly are low in relation to scores on the verbal subtests of Comprehension, Information, Arithmetic, and Similarities. Studies are cited as showing a similar but less extreme pattern in Protestant children and an even less extreme pattern in Catholic (Irish and Italian) children. Dershowitz and Frankel related these patterns to Witkin's (1967) concept of psychological differentiation. According to their hypothesis, Jewish subjects are less psychologically differentiated than Protestant or Catholic subjects.Even though low levels of psychological differentiation have been shown to be related to poor performance on three of the subtests on which Jewish subjects exhibit relative deficits, Dershowitz and Frankel (1975) themselves admit that they are unable to account for the poor Picture Arrangement scores of Jewish subjects with this explanation. Further, they cite only one unpublished study (Litman, Requests for reprints should be sent to Colin Martindale,