Mental health nurses are the largest cohort of clinicians working in Irish Mental Health services, and are usually involved in the care of service users experiencing acute psychosis either as in-patients, mental health community facilities or in the service users own home. Some service users place value on communication with nurses as it helps with easing their difficulties (Gilburt, Rose and Slade 2008; Russo and Hamilton 2007, however others report not been listened to, ignored and disempowered (Octwell and Capital Members 2007). In addition, both groups worry about risk and vulnerability when communicating with each other (Norwood 2007;Duxbury and Whittington 2005).Consequently, understanding the process of how these two groups manage to communicate together is worthy of study as research into this area is limited. Hence, this Classic Grounded Theory study aimed to address these gaps by developing a substantive theory pertaining to the phenomena of communications between nurses and service users experiencing acute psychosis that could be used to inform mental health nursing practice (Glaser and Strauss 1967). This involved interviewing sixteen participants, seven nurses and nine service users who had experienced acute psychosis, and getting their views about communicating together. The study led to the development of a substantive theory that explains how they established what constituted permissible communication for period in time through the processes of guardedness in communications. The theory incorporated a dynamic psychosocial process where nurses and service users moved from raising to lowering guardedness and vice versa depending on their sense of risk, attempts to ease distress, or consider that it is advantageous to raise or lower their guard. This was a complex and interactional process which was influenced by past experiences, current events, contexts and how nurses and service users presented when communicating. This guardedness in communications also facilitated a sense of ownership and control over what they say and do. It is proposed that mental health nurses and service users can use appropriate guardedness to establish what they consider are permissible communications at a moment in time, in order to enhance their understandings of how they communicate together and hopefully to make a difference for service users experiencing acute psychosis.