The determination of boron in animal organ tissues using inductively coupled plasma atomic emission spectroscopy (ICP AES) has been optimized for analytical support of boron neutron capture therapy of cancerous tumors. The proposed technique is universal and rapid. The methodology includes: preliminary acid decomposition at elevated temperatures and pressure (if necessary), determination of boron by ICP AES in the obtained solutions using reference samples based on single-element solutions. The method is verified by spike experiment and varying the weight-samples. The ICP AES technique was used to evaluate the accumulation of boronophenylalanine and borocaptate in mice organs. Biodistribution of 10B in the case of intravenous administration of the drug to SCID mice with SPF status using the human glioblastoma cell line U87 was investigated.