Smooth pursuit eye tracking impairment has been observed in the major psychoses, particularly schizophrenia. To understand better the relationship of smooth pursuit disruption to personality dispositions linked to psychiatric syndromes and to two other "marker variables" associated with psychosis (low platelet monoamine oxidase [MAO] activity and poor performance on the continuous performance task [CPT]), we studied the psychologic, biochemical, and psychophysiologic correlates of impaired smooth pursuit tracking in two nonpsychiatric patient populations. One sample consisted of 67 volunteers screened for extreme values in a distribution of platelet MAO activities, and the second included 29 volunteers screened for extreme scores on the CPT. An aggregate of about 5% of both samples showed clearly dysfunctional smooth pursuit. Eye tracking dysfunction did not seem to be related to either MAO or CPT performance in either study. Both studies were consistent in showing that subjects with impaired smooth pursuit eye tracking had a psychologic profile characterized particularly by social introversion.