Tumours are examined in a simple sandwich structure which gives the samples a well defined shape and volume. Collimated light is scattered by the sample and analysed using a goniometer. It is found that tumours can be optically characterized by only two parameters. In phantoms, composed in order to approach closely the optical properties of tumours, a relationship is established experimentally between these parameters and the penetration depth. Using this relationship the penetration depth in tumours can be determined for 630 nm and 680 nm wavelength light.