The influence of social relations on the development of species recognition ('sexual imprinting') in zebra finch (Z) males was examined. This was done with Z males raised by mixed pairs of Z and Bengalese finches (B)(♂Z♀B or ♀Z♂B). During rearing, the behaviour of parents and sibling towards the young Z males was measured. Z males raised by mixed pairs were usually exposed to more parental behaviour, contact behaviour and aggression by Z (parent and sibling) than by B. These males also preferred a Z over a B female later on, which might be a consequence of differences in behavioural interactions with Z and B. In a series of experiments the amount of different behaviour patterns shown by the Z parents towards young Z males was decreased. This led to a shift from Z to B in the later preference of these males, in spite of the fact that 'visual exposure' to Z was maintained as much as possible. Influence of the sibling was examined by comparing the preference of Z males raised with a B sibling with that of Z males raised with a conspecific sibling. The effect of the sibling on the later preference, if any, appeared to be marginal to that of the parents. Preference differed between males raised by ♀ Z♂B pairs and males raised by ♂Z♀B pairs, the latter being more B directed. Experiments indicate that this difference is most likely due to lack of familiarity with female Z characteristics in males raised by ♂Z♀B pairs. The results strongly suggest that behavioural interactions between a young Z male and other birds, rather than visual exposure only, influence the later preference of this male. Several mechanisms which might underlie this effect on the developmental process are discussed. No initial preference for Z characteristics has to be assumed to explain that Z males raised by mixed pairs normally develop a Z directed preference.