The production of sulfate via multiphase chemistry is usually assumed to be dominated by oxidation of S(IV) by O3 and H2O2. The former reaction is pH dependent and negligibly small for pH less than about 5, while oxidation via H2O2 is independent of pH. Another oxidant that may play a role in sulfate formation is NO3 <Sander et al., 1995; Mozurkewich, 1995; Rudich et al., 1998>. Although it is commonly assumed to be far less important than O3 and H2O2, it has been hypothesized that it may account for significant oxidation under certain conditions, such as relatively low mixing ratios of O3 and <150 pptv of H2O2. These conditions may be met in the nighttime Northern Hemisphere winters when H2O2 production is small and NOx concentrations are sufficient to produce adequate concentrations of NO3. We explore the importance of NO3 in multiphase sulfate production using a simple cloud model. It is shown that the relative importance of NO3 is very sensitive to the assumed value of the Henry's Law equilibrium constant of NO3 as well as the assumed catalytic chain length for NO3 oxidation of S(IV). Using the recently measured value of 0.6 M atm-1 <Rudich et al., 1996>, and a catalytic chain length of 8, it is shown that NO3 enhances sulfate production by about 10--30% relative to calculations where NO3 is absent. It is noted that NO3 may contribute even more if additional sources of NOx are present and/or H2O2 is removed via precipitation.