This paper reports on a method for determination of the optical properties of bread. The optical properties of white bread have been studied. The measurements were carried out for dough, crumb and crust. The transmission and reflection measurements were made with a Beckman spectrophotometer with an integrating sphere. Transmission functions and penetration depths were calculated and compared with previous investigations made at this institute (SIK). The influence of peak power wavelength and spectral range (800-1250 nm and 1250-2500 nm) on the penetration depth for crust and crumb have been determined. This study has shown that it is possible to calculate penetration depth for any radiator using transmission data in the range 800-2500 nm. © 1989.