Decision-making strategies used by nurses in telephone triage involving public emergency calls for medical help were investigated as a function of task urgency and complexity in the real-world dynamic environment. The sample included 34 nurses as call receivers. Transcripts of 50 nurse-client dialogues and 50 explanations of the decision-making process, elicited immediately after completion of the calls, were analyzed using methods of discourse and protocol analyses. In high-urgency situations, heuristic rules based on symptoms were used, and the decisions were mostly accurate. With the increase in problem complexity, more causal explanations were found, and the decisions were more often inaccurate. Furthermore, the explanations supporting the accurate decisions were often inaccurate, showing a decoupling of knowledge and action. Alternate strategies were used in moderate- to low-urgency conditions, where contextual knowledge of the situations was exploited to identify the needs of the clients and to negotiate the best plan of action to meet these needs, resulting in more accurate decisions.