SummaryThe ability of aerobic and anaerobic spores, after various degrees of heating, to produce macrocolonies in media containing different concentrations of sodium chloride, potassium nitrate and sodium nitrite has been examined. The effect of different heat treatments, roughly fromF0= 0.0015 toF0= 1.5, on the inhibitory levels of these curing ingredients, showed that the more severe treatments were capable of rendering surviving spores considerably more sensitive to subsequent inhibition by concentrations of the order found in cured meats. To produce this effect, less heating was needed with twoBacillusstrains than with three ofClostridium. Sodium chloride and potassium nitrate had quantitatively similar effects. The inhibitory effect of sodium nitrite increased roughly ten‐fold from pH 7 to pH