The recombination reactions HO+NO+M double right arrow HONO+M(1) and HO+NO2+M double right arrow HNO3+M(2) have been investigated over an extended pressure (1-1000 bar) and temperature (250-400 K) range. HO radicals were generated by laser flash photolysis of suitable precursors and their decays were monitored by saturated laser-induced fluorescence (SLIF) under pseudo-first-order conditions, The measured rate constants were analyzed by constructing falloff curves which provide the high pressure limiting rate constants k(infinity). In the given temperature range, these rate constants are k(1 infinity) = (3.3+/-0.5) x 10(-11) x (T/300 K)(-(0.3+/-0.3)) and k(2 infinity) = (7.5+/-2.2) X 10(-11) cm(3) molecule(-1) s(-1).