We studied the relationship between the predisposition to major psychoses and the level of self-reported experiences of heterosexual behaviour in 153 secondary students. 'Normal' equivalents of Schizotypal and Borderline Personality Disorders were assessed respectively by the Schizotypal Personality (STA) and Borderline Personality (STB) scales introduced by Claridge and Broks (1984). The level of self-reported heterosexual behaviour was assessed by means of a modified version of the Guttman scale developed by Bentler (Garcia-Sevilla, Muntaner, Moreno and Trullas, 1984). Results showed a significant positive relationship between the level of heterosexual behavior and STB. No significant relationships were found with STA. The potential significance of these findings in order to validate STA and STB scales is discussed. © 1987.