Clinical reports rave about the efficacy of sublingual morphine, but most research data suggest that sublingual morphine lacks the necessary physical characteristics to be absorbed through sublingual tissues. This article clarifies these assertions by reviewing the clinical literature that supports sublingual administration, the theories relevant to sublingual morphine administration, and the pharmacokinetic research that supports or negates the benefit of this route. Recommendations for clinical nursing practice are provided to guide decision-making in care of patients with cancer pain.