Pain assessment and management are complex issues that embrace physiological, emotional, cognitive, and social dimensions. This observational study sought to investigate nurse-patient interactions associated with pain assessment and management in hospitalized postsurgical patients in clinical practice settings. Twelve field observations were carried out on Registered Nurses' activities relating to pain with their assigned patients. All nurses were involved in direct patient care in one surgical unit of a metropolitan teaching hospital in Melbourne, Australia. Six observation times were identified as key periods for activities relating to pain, which included change of shift and high activity periods. Each observation period lasted 2 hours and was examined on two occasions. Four major themes were identified as barriers to effective pain management: nurses' responses to interruptions of activities relating to pain, nurses' attentiveness to patient cues of pain, nurses' varying interpretations of pain, and nurses' attempts to address competing demands of nurses, doctors and patients. These findings provide some understanding of the complexities impacting on nurses' assessment and management of postoperative pain. Further research using this observational methodology is indicated to examine these influences in more depth. This knowledge may form the basis for developing and evaluating strategic intervention programmes that analyse nurses' management of postoperative pain and, in particular, their administration of opioid analgesics.