In order to standardize methodologies that allow to determine the concentration of nitrifying and denitrifyingbacteria in compost, bacteria growth was evaluated at two different concentrations of nitrogen substrate(NH 4)2 SO4 and KNO3), with and without calcium carbonate. Technique used was the most probablenumber (MPN), revealing the tubes by means Griess reagent (nitrite), Nessler reagent (ammonium), andthe zinc powder (nitrate). Four treatments for nitrifying and denitrifying bacteria were applied respectively,with concentrations of 0,5 or 0,33 g of (NH4) 2SO4 and 0,5 or 2g of KNO3. Biomass production wasevaluated. No significant differences were evidenced in biomass of days14 th,15th and 16th for nitrifyingbacteria; however, 15 th day 115.88 MPN/g of compost was obtained for nitrifying bacteria, and 31.42MPN/g for denitrifying bacteria. Treatment 1 (0.5g of (NH4)2SO4 with 1g of CaCO3) in nitrifying and 0.5gof KNO3 with 5g of CaCO3 in denitrifying group represent the best biomass condition: 112.67 MPN/g and27.53 MPN/g of compost. 15 days were necessary for incubation because it is the time needed to activateenzymes regulating pH with addition of the CaCO3.