We report the observation of cavity‐induced modifications of the three‐dimensional bulk exciton emission in a planar GaAs microcavity, in which the entire cavity layer is an active material. We have performed standard photoluminescence measurements at various emission angles, obtaining evidence of coupling between the exciton and the cavity mode. The modified density of photon states available for the exciton decay shows up in the angle dependence of the emission lineshape, as well as of the photoluminescence peak intensity. The experimental results are qualitatively clarified with theoretical calculations performed with an adapted transfer‐matrix approach. ©1995 American Institute of Physics.