The objective of the paper is to determine the optimum preincubation time after rewetting of dried soil for estimating soil microbial biomass (SMB) and to identify a quick, reliable biochemical predictor of soil N mineralization potential. Biochemical determinations of SMB were screened on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) having five levels of soil organic C as a result of long-term management. Biochemical determinations included arginine ammonification, substrate-induced respiration, cumulative C and net N mineralization, and SMBC using the chloroform fumigation-incubation (CFI) method. The CO2-C evolved during the first day after rewetting of dried soil is recommended for rapid estimation of SMBC and potential N mineralization because of its simplicity and precision.