The effects of magnetic fields up to 20 T were studied in CuInSe2 single crystals using photoluminescence (PL) at 4.2 K. Diamagnetic shifts of the free A and B excitons measured in the PL spectra in CuInSe2 at 4.2 K under the magnetic fields were used to estimate the reduced masses (0.095m0 for the A and 0.098m0 for the B exciton), binding energies (7.0 meV for the A and 7.2 meV for the B exciton) and Bohr radii (7.6 nm for the A and 7.3 nm for the B exciton) of the free-excitons in CuInSe2 assuming that both excitons are isotropic and hydrogen-like. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)