The efficacy of 10 ppm phenylmercuric acetate (PMA), 2N KCl and 0.02N CuSO4in suppressing ammonification, denitrification and CO2accumulation was studied during short‐term anaerobic incubations of three soils at 25 C. KCl and CuSO4almost completely suppressed ammonification in two of the soils and decreased it markedly in the third. Ammonification was suppressed to a lesser extent by the addition of PMA. The KCl treatment was much more effective than either PMA or CuSO4in preventing NO3‐disappearance and denitrification. Appreciable amounts of NO3‐disappeared from the soils treated with PMA and CuSO4. N2and not N2O was the major denitrification product; the suppressors had only a small effect on N2O accumulation. The influence of the chemicals on CO2accumulation differed according to the soil. CuSO4was least effective at depressing the accumulation of CO2, and, in fact, stimulated it in one soil. Neither 0.02N CuSO4nor PMA (10 ppm) is recommended in the absence of a concentrated salt solution for preventing mineral nitrogen changes during extraction of inorganic soil nitrogen. The value of 2N KCl in suppressing such changes is emphasized by the results of the present study.