The lattice parameters of synthetic diaspore (AlO(OH)) and synthetic and natural corundum (Al2O3) have been measured at simultaneously elevated pressure and temperature up to 7 GPa and 800 ¿C (1000 ¿C for corundum) using a MAX 80 cubic anvil high-pressure apparatus. Several experimental runs were carried out for both minerals, in which the samples were first compressed at room temperature and then heated; NaCl served as an internal standard for pressure calibration. In most runs the samples were mixed with Vaseline or NaCl to ensure hydrostatic pressure-transmitting conditions. Some runs, mainly at pressures <4 GPa, were performed without using a pressure medium. A Birch-Murnaghan equation of state (EOS) was fitted to the experimental data obtained at room temperature (assuming K'=4), yielding bulk moduli K(diaspore)=134.4¿1.4 GPa in contrast to 230 GPa obtained from diamond anvil cell measurements without using a pressure medium recently, and K(corundum)=219.1¿3.5 GPa, consistent with previous results based on X-ray diffraction measurements in conjunction with multi-anvil high-pressure techniques. The high-temperature Birch-Murnaghan EOS was fitted to the high-temperature high-pressure diaspore data, P=1.5KTT,r-7-VT,r-5><1-0.75(4-KT')(VT,r-2-1)>, VT,r≡(V/VT,0)1/3, KT=K+(∂KT/∂T)P(T-298.15), VT,0=117.84 ¿3 exp(∫a+bTdT), resulting in K=133.6¿4.0 GPa, KT'=4.1¿1.5, (∂KT/∂T)P=-0.017¿0.007 GPa K-1, a=2.22¿0.40 10-5 K-1, and b=2.23¿0.79 10-8 K-2. ¿ 2000 American Geophysical Union