A simple Pt electrode was used to determine the electrical conductances of 0.00393, 0.00992 and 0.0379 m NaNO3 and 0.00911 m LiNO3, 0.00910 m CsNO3 and 0.00946 m Ca(NO3)(2) solutions. Temperatures ranged from 25 to 505 degrees C at pressures ranging from 100 to 490 bar. The electrode was calibrated against the conductance of 0.010 m hydrothermal NaCl solutions. Preliminary limiting equivalent conductances and dissociation constants were obtained for hydrothermal NaNO3 solutions. The alkali nitrate series behaved similarly to the alkali chloride series: the electrical conductance decreases with decreasing cation radius. This seemingly paradoxical result is due to the stronger electric held and hence the greater tendency for ion pairing and larger solvation spheres associated with smaller cations. Nearly complete ion association is observed at low-density supercritical conditions. Maximum conductances were obtained at about 300 degrees C and densities increasing from about 500 kg m(-3) to 725 kg m(-3) with increasing concentration. Limiting conductances and pK(a) values for NaNO3 solutions were similar to those for NaCl solutions, with NaNO3 being the weaker electrolyte. Ca(NO3)(2) conductances follow similar trends to K2SO4. The data suggests that nearly complete dissociation occurs below 200 degrees C, but that appreciable association to form monovalent cations occurs at higher temperatures.