Two modifications of the hydrothermal diamond anvil cell (HDAC) have been made, the first for transmission XAFS (X-ray absorption fine structure) analyses and the second for fluorescence XAFS analyses of elements with low absorption edge energies. In the first modification, laser-drilled holes in the diamond anvils reduce the X-ray path-length in diamond to 300 µm in order to minimize the attenuation of X-rays due to absorption and scatter. In the second modification, laser-machined cup and grooves in one of the diamond anvil faces reduces the X-ray path-length in diamond to 160 µm and permits a 90° take-off angle. Both modifications can be used to obtain XAFS spectra on aqueous solutions of first-row transition elements as well as rare earth elements at elevated temperatures and pressures. The second modification is capable of measurements on solutions of concentrations in parts per million (ppm) range. These techniques are being used for carrying out experimental measurements valuable in the interpretation of fluid inclusions in minerals found in ore-forming hydrothermal systems as well as other important lithospheric processes involving water.