Odours are judged to smell sweeter following simultaneous oral pairings with the tastant sucrose and sourer after parings with the tastant citric acid. This effect may result from human participants perceiving and encoding a unitary odour-taste percept. This study examined two factors thought likely to disrupt such encoding; (a) preexposure to the mixture elements and (b) training to spot the elements of taste-odour mixtures. Half of the participants were trained to identify tastes and smells and half received no training. All participants were preexposed to two odours (A, B) and two tastes (X, Y), followed by pairings of these stimuli (AX, BY) and then by pairings between two non-preexposed odours and the same tastes (CX, DY). This process was then repeated on a second session. Odour-taste learning was retarded following preexposure, but was unaffected by training. These findings suggest; (1) that odour-taste mixtures may be cognitively impenetrable and (2) that preexposure leads to encoding of A and B, which are then resistant to interference when further pairings are presented (i.e. AX, BY).