Cavity and sentinel lymph node marking devices, marker delivery devices, and methods are disclosed. More particularly, upon insertion into a body, the cavity marking device and method enable one to determine the center, orientation, and periphery of the cavity by radiographic, mammography, echogenic, or other noninvasive imaging techniques. A composition and method are disclosed for locating the sentinel lymph node in a mammalian body to determine if cancerous cells have spread thereto. The composition is preferably a fluid composition consisting of a carrier fluid and some type of contrast agent; alternatively, the contrast agent may itself be a fluid and therefore not need a separate carrier fluid. This composition is capable of (1) deposition in or around a lesion and migration to and accumulation in the associated sentinel node, and (2) remote detection via any number of noninvasive techniques. Also disclosed is a method for remotely detecting the location of a sentinel node by (1) depositing a remotely detectable fluid in or around a lesion for migration to and accumulation in the associated sentinel node and (2) remotely detecting the location of that node with a minimum of trauma and toxicity to the patient. The composition and method may serve to mark a biopsy cavity, as well as mark the sentinel lymph node. The marking methods also may combine any of the features as described with the marking device and delivery device.