Phenylboronic acid (PBA) derivatives, which are often termed boronolectins,' are regarded as a synthetic mimic of lectins because of their ability to interact with various carbohydrates. This unique chemistry has already borne fruit as the molecular bases for glucose sensors and some bio-separation applications. This focus review highlights some of the emerging PBA-based research directions toward more versatile diagnostic and therapeutic targets, which the authors are currently pursuing. The topics reviewed include PBA-mediated targeting to sialic acid (SA) as a methodology relevant to tumor diagnosis and treatment. Other drug delivery systems, including those for siRNA and insulin, in which PBA has a unique role in physicochemical signal transduction, will also be summarized.