In natural rearing conditions, the social environment of lambs includes the mother, age-mates and other members of the flock. Lambs rapidly develop the ability to discriminate between individual conspecifics or members of different social categories. In the present study recognition among familiar unrelated lambs was assessed in a series of tests. At first, the lambs and their mothers were housed together in small groups for 1 week (Original groups; O). After that they were reorganized into new groupings (Recent-groups; R) for the remainder of the experiment. During test series 1, lambs that were paired with a familiar O-group partner, from which they had been separated for 5 days emitted fewer distress bleats than did those tested with an unfamiliar partner. Two days after this test, when the lambs were given a choice between an O- versus a R-partner, lambs did not display a preference for either of the stimulus lambs. However, in an additional two-choice test the subject lambs responded discriminatively to a recent familiar partner that was simultaneously present with an unfamiliar lamb. In summary results of this study suggest that lambs are capable of developing discriminative relationships with age-mates from different sub-groups, and that such social discrimination persists over a separation period lasting at least several days.