The reactions of NO+ and NO2+ with water are considered to make an important contribution to the formation of proton hydrates in the upper atmosphere. There have been several-recent studies of the; relevant reactions, with the result that discrepancies have arisen in each case over the critical number of water molecules required to promote the appearance of a proton hydrate, Presented here are new results based on the collision-induced reactions of NO+.(H2O)(n) and NO2+.(H2O)(n) cluster ions, which we believe clarify the situation.