Aqueous diffusivities and solubilities of NO were determined by using a chemiluminescence detector to measure time-dependent fluxes across stagnant liquid films confined between polydimethylsiloxane membranes. The NO diffusivities in pure water and PBS at 25 degrees C were found to be (2.21+/-0.02) x 10(-5) cm2 s(-1) and (2.21+/-0.04) x 10(-5) cm2 s(-1), respectively. Although lower than most previous values for NO at room temperature, these diffusivities are very similar to those for O2, as one would expect. Extrapolation to 37 degrees C yielded a value of 3.0 x 10(-5) cm2 s(-1). The solubility of NO in water at 25 degrees C was (1.94+/-0.03) x 10(-6) mol cm(-3) atm(-1), in agreement with the literature. This agreement, along with the excellent fits obtained to the transient flux data (<4% rms error in each experiment), supports the validity of the simultaneously measured diffusivity. The solubility of NO in PBS at 25 degrees C was (1.75+/-0.02) x 10(-6) mol cm(-3) atm(-1). The modest (10%) reduction in solubility relative to that in pure water is consistent with the usual effects of salts on gas solubilities.