The survey of researches within social identity theory (Tajfel, 1985) and self-categorization theory (Turner et al., 1987) shows that studies in this area are mostly concerning intergroup behavior between wide social groups. This study describes categorization processes rising up in the discourses of a small group interacting in a natural context. Data have been extracted from conversational transcriptions of 5 work meetings; collective pronouns (GRE: Group Referring Expressions) have been used as markers of social categorization processes. Main results show that: 1) members of the group use a wide range of self- and other-referring expressions showing a complex social categorization (not simply reduceable to ingroup-outgroup opposition); 2) intra-group differentiation is more remarkable than integroup one; 3) discoursive contents have an effect on the esplicitation of social categorization markers. Conversational analisys shows also that social categorization is a result of negotiation processes and argumentative choice of group members more than a static trait of their identity.