To combine human factors engineering techniques with qualitative observation of nurses in practice to analyze the nature of nurses' cognitive work and how environmental factors create disruptions that pose risks for medical errors. Few researchers have examined the nature of nurses' cognitive work while in practice with patients. Researchers have described the broad range of thinking processes required in the acute care work setting, but have failed to examine how such processes are conducted and influenced by the complex care environment. A combined research methodology enables researchers to better understand how the nursing process becomes disrupted and the potential influence of this disruption on the safe and effective care of patients. An ethnographic study, using mixed-methodological approaches, involved 7 staff registered nurses. The quantitative and qualitative data collection included field observation and summarative interviews.