Background Medical Emergency Teams (METs) have been developed and implemented with the aim of improving recognition of and response to deteriorating patients. Yet, METs are often not activated or used effectively by nursing staff. The reasons for this are not fully understood. Objectives The aim of this study was to explore nurses' experiences and perceptions of using and activating a MET, in order to understand the facilitators and barriers to nurse's use of the MET. Design, setting and participants An interpretive qualitative approach was adopted to explore nurses' experiences and perceptions of using and activating the MET. This study was set in a large public teaching hospital in Southeast Queensland, Australia. Fifteen registered ward nurses who had cared for patients who had deteriorated on the ward, and as a result of this deterioration were admitted to the Intensive Care Unit (ICU) as an unplanned admission, were interviewed about their experiences and perceptions of using a MET. Methods In-depth, semi-structured interviews were conducted with ward nurses who had cared for a patient who had deteriorated. Interviews were recorded and transcribed verbatim. The interviews were analysed thematically. Findings Four themes relating to the participants' experiences and perceptions of using a MET emerged from the data. These themes were: (1) sensing clinical deterioration; (2) resisting and hesitating; (3) pushing the button; and (4) support and leadership. Conclusion This work identifies why nurses do not activate METs appropriately. This delay in MET activation potentially exposes the deteriorating patient to suboptimal care and increases the risk of adverse events.