This study explored the sources of knowledge that intensive care nurses used in their daily nursing practice. It used a qualitative design based on four focus group interviews with 20 intensive care nurses, from four intensive care units in Norway. Data were analysed using systematic text condensation. The following condensed meaning units were identified: research, theoretical knowledge, experiential knowledge, work place culture, clinical expertise and patient participation. This study illustrates the complexity and variety of the knowledge bases of intensive care nurses. Despite some variation in nurses' familiarity with research literature, nursing interventions found by research to be useful were given priority, and research affected daily practice through changes in guidelines and procedures.