The Studsvik thermal-neutron facility was originally designed for neutron capture radiography (NCR) at high thermal-neutron fluence and low fast-neutron contamination. It has now been modified to permit irradiation of living cells and animals without the need for stopping and restarting the R2-0 reactor. Previous calculations of the thermal-neutron intensity at the NCR position were performed using the two-dimensional diffusion theory code DIXY. In this report the Monte Carlo program MCNP 3B is used to calculate the neutron fluence at the radiography position, and neutron and photon fluences at the positions of the cell specimens. The normalized neutron fluences from the calculations agree well with measured values and show that the contamination with high-energy neutrons is low. The agreement between measured and calculated photon doses was reasonable. The thermal-neutron fluence rate is (2.3 +/- 0.1) x 10(9) cm-2 s-1 at 100 kW at the NCR position and (0.96 +/- 0.03 x 10(9) cm-2 s-1 at 100 kW at the front plate of the loading tube. The photon dose is about (1.6 +/- 0.2) x 10(-12) Gy per neutron. Survival curves of V79 cells grown as monolayers and irradiated in the thermal neutron beam, with and without boron, are presented.