The recognition of the importance of lymphoscintigraphy for identification of the sentinel lymph nodes in melanoma and breast cancer plays a significant role in the clinical management of these patients. The widespread clinical acceptance of this technique and the lack of an agreement on which radiopharmaceutical agent has the most ideal properties has resulted in a wide variety of agents being used clinically with other agents under investigation or development. This article reviews some of the physical properties that a radiopharmaceutical agent should possess and discusses in depth commonly used agents and lists some agents under development. This article also discusses the dosimetry and biological effects various radiopharmaceutical agents have for lymphoscintigraphy in melanoma and breast cancer patients. In view of the lack of a consensus agreement on which radiopharmaceutical agent will provide the optimal clinical information this article will provide an overview of potentially useful radiopharmaceutical agents and radiation dosimetry considerations.