On Saturday, November 23, 1963, the day after John F. Kennedy had been assassinated, a six-hour battery of cognitive and personality measures was administered to a sample of 58 undergraduates at a small eastern college. Three months later, another comparable sample from the same college was administered the same battery for comparison purposes. The effects of the assassination on cognition and personality were found to be fairly specific. In terms of overall main effects, all three marker tests for flexibility of perceptual closure were implicated, along with a measure of the speed of closure factor. Experimental subjects were also found to be more indifferent than comparison subjects in their affective reactions to stimuli and tended to be more constricted in graphic expression. Several significant interactions were also observed with sex of subject and with birth order, and these interactions primarily involved these same variables--measures of the two factors of speed and flexibility of perceptual closure, of graphic constriction-expansiveness, and of indifference in affective reactions to stimuli. The effects of the assassination on personality scales were also quite specific. Experimental subjects were significantly more yielding and conventional than comparison subjects, but at the same time were more dogmatic and extreme in expressing opinions.