Purpose - This paper aims at contributing to the debate on organisational citizenship behaviour (OCB) by developing a theory-driven measure of cooperative behaviour within organisations, called organisational solidarity (OS). Design/methodology/approach - Data are gathered through a survey among 674 employees from nine organisations. Scales are constructed using the multiple group method. OLS regression is used to test the hypotheses. Findings - The data analyses show that reciprocity is an important mechanism to bring about cooperation within organisations. Based on this, a distinction is made between horizontal and vertical OS. Research limitations/implications - The major shortcoming of this research is that some of the results may be influenced by same source bias. The research implies that cooperative types of employee behaviour - such as OCB - depend on the behaviour of others. Furthermore, these kinds of behaviour can be divided into a horizontal and a vertical dimension. Practical implications - The findings suggest that supervisors can play a facilitating role in creating and sustaining cooperative behaviour of employees. Originality/value - This paper contributes to the literature on OCB by examining how this kind of behaviour is affected by the behaviour of supervisors and co-workers. Secondly, whereas other articles focus on either horizontal or vertical dimensions of cooperative behaviour, this paper focuses on both dimensions simultaneously.