We have investigated the photoluminescence spectrum of self-assembled InAs quantum dots embedded in a GaAs matrix in magnetic fieldBup to 23 T and under hydrostatic pressure up to 8 kbar. A strong anisotropy in the diamagnetic shift is found depending on whetherBis applied parallel or perpendicular to the growth direction. In the former case, the spatial extent of the carrier wave function in the dot is estimated to be 60 Å. The pressure coefficient for the dot emission line is (9.1±0.2) meV/kbar, about 20&percent; smaller than for the &Ggr;-point band gap in bulk GaAs. ©1997 American Institute of Physics.