Task alternation takes the form of a periodic exchange of jobs between two or more operators. Most authors believe this to represent an attempt to balance the workload between individuals. In this article, we consider the precise determinants of this phenomenon. Field studies indicate that the phenomenon occurs when members of the team have different roles, all with different requirements. These characteristics lead us to consider two explanations of the intra-individual nature of task alternation. The difference in roles suggests that this might be due to a desire for variety in professional life. Focusing on requirements leads us to think of task alternation as a response to the exhaustion of an individual's resources. However, task alternation also seems to be characterized by virtually fixed intervals at which such “job swaps” are made, perhaps as result of social influences and a tendency towards behavioural standardization. This latter explanation is inter-individual in nature. To test these hypotheses, we conducted three experiments which, placing teams consisting of two subjects each in a situation in which they had to perform two different tasks over a period of an hour. The subjects were free to decide how to manage the work. In the first experiment we observed that task alternation took and place the changeovers were preceded by a decline in performance. However, alternation was periodic within each group and the groups exhibited different rotation rhythms. These results therefore support an explanation both in terms of the exhaustion of resources and social influence. The two subsequent experiments, in which a real or fictitious colleague was introduced into each team showed that subjects respected a period of introduction before asking colleagues to swap tasks and that this period influenced both their behaviour and their representations of the tasks. Overall, the results suggest that a norm of equity is generated in each group and it is this which plays a dominant role in task alternation. This is discussed in the light of criticisms levelled at the models of individual functioning, which have, at the very least, to be extended to take account of collective activities.