The present study compared the impact of symbolic equivalence and opposition relations on fear generalisation. In a procedure using nonsense words, some stimuli became symbolically equivalent to an aversively conditioned stimulus while others were symbolically opposite. The generalisation of fear to symbolically related stimuli was then measured using behavioural avoidance, retrospective unconditioned stimulus expectancy and stimulus valence ratings. Equivalence relations facilitated fear generalisation while opposition relations constrained generalisation. The potential clinical implications of symbolic generalisation are discussed.