Boron neutron capture therapy (BNCT) is an experimental radiation therapy that is being developed for the treatment of malignant tumors. One requirement for successful BNCT is that a sufficient amount of 10B concentrates in the tumor while clearing from normal tissues and blood. Many pharmaceuticals are currently being developed to selectively deliver 10B to a tumor. To evaluate the effectiveness of various 10B delivery agents, the concentrations of boron in blood, tumor, and normal tissues must be known. Using the solid-state nuclear track detector CR-39, a tissue assay technique has been developed to spatially determine 10B concentrations in tissue samples. The technique has been used to quantify 10B concentrations in tumor and normal tissue on lines across rat brain tissue sections. This was done by combining 10B concentrations measured on lines across the CR-39 with color digital images of the tissue section. Coupling the methodology that was developed for tissue samples with an existing analytical technique for blood-10B concentration measurements allows for complete evaluation of 10B distributions in blood, tumor, and normal tissues and should be useful in evaluating various 10B delivery agents for use in BNCT.