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.