Individual hemisphericity of nonparanoid schizophrenics, depressives, manicdepressives, schizo-affectives, alcoholics, and subjects with personality disorders (antisocial type) was compared by utilizing the conjugate lateral eyemovement index. In a total population of right-handed males (N = 100), 45% were found with right hemisphericity, 41% with bilaterality, and 14% with left hemisphericity. Right hemisphericity was found associated with nonparanoid schizophrenia, depression, and alcoholism; bilaterality was found to be related to manic-depression, schizo-affective disorder, and antisocial personality.Investigations of commissurotomy patients and patients with unilateral brain damage have shown consistently that the two cerebral hemispheres tend to be specialized for cognitive function, modes of processing data, and linguistic role (Bogen, 1969a(Bogen, , 1969bGazzaniga, 1970). Subsequent studies with intact subjects provided additional support for the theory of hemispheric lateralization for cognitive mode Kinsbourne, 1972;Kocel, Galin, Ornstein, & Merrin, 1972). The two cerebral systems have been found to interfere with one another on performance of certain tasks by sending out conflicting signals (Gazzaniga, 1973).Although studies have shown that people tend to utilize the hemisphere most appropriate for a given task (Galin & Ornstein, 1974), there is some evidence for the existence of "individual hemisphericity," that is, a tendency to rely most heavily on one mode in preference to the other, whether or not the preferred mode is the more appropriate for the task at hand (Bogen, DeZure, TenHouten, & Marsh, 1972). The actual ratio in the general population of the three possible hemisphericity types, right, left, and "bilateral," is apparently unknown, although approximately equal numbers of right and left types have been reported (Bakan, 1971; Day, 1967a). This article is based on a dissertation submitted by the first author in partial fulfillment of the requirements for the PhD degree at the University of Southern Mississippi. Thanks are extended to Robert Heath and James Hurst for the encouragement derived from their interest in this study.