Purpose: The purpose of the paper is to contribute to an understanding of the relational work carried out in mentoring programmes and the implications for learning capabilities in future practices. Design/methodology/approach: This study is based on field research of a mentoring programme bringing together senior and newly graduated workers in a large Swedish health care organisation. In total, 54 qualitative interviews with mentors, mentees, HR, managers and union representatives are included. Findings: The findings point to the role of trust and a psychological sense of community in the socialisation work that goes on in relationships between the mentor and the mentee. This in turn leads to increased social capital in the form of learning and retaining workers. The conditions for being vulnerable and asking questions, as well as daring to be independent, are an essential and decisive part of constructing bonding within the professional group and bridging out to other professions and parts of the organisation. Practical implications: The practical contribution from this study is the workplace conditions that are central to organising mentoring programmes, with implications for learning capabilities in future practices. Originality/value: With its theoretical focus on social capital, the study shows the importance of relationships for learning and retaining both newly graduated and experienced employees in a context of high employee turnover. It is central to achieving strong and mutually beneficial relationships through continual and trustful interaction between actors. By using the concepts of social capital, socialisation agents and psychological sense of community, this study contributes to an understanding of mentoring and workplace learning.