Purpose: To obtain more accurate information on the dose distribution in rhesus monkeys for total body irradiation with orthovoltage X-rays. Materials and methods: Dose measurements were performed with an ionization chamber inside homogeneous cylindrical and rectangular phantoms of various dimensions and in phantoms containing lung-equivalent material. The irradiations were carried out with reference to a monitor ionization chamber placed alongside the phantom or the irradiation cage. Results: Correction factors for mass and lung dose relative to the average close in a homogeneous reference phantom, showed linear relationships with the effective diameter of the monkey. The lung close correction factor relative to the homogeneous phantom was about 1.12 for a 3.5 kg monkey. The stated values for the average absorbed dose in the animal of standard weight should be multiplied by a factor of 0.93 for experiments performed before 1983. All publications on total body irradiations of monkeys at TNO after 1983 contain the corrected dose values. Conclusion: Dose distributions are reported for phantoms of different diameters and of cylindrical or rectangular shape. The new dosimetry has also resulted in a revised statement of the LD50 for the occurrence of bone marrow syndrome after X-irradiation; 4.9 Gy instead of 5.3 Gy.