Microbial biomass and respiration kinetics were monitored in a soil from the central Negev Desert, Israel. The chloroform‐fumigation‐incubation (CFI) and the substrate‐induced respiration (SIR) method were used to estimate microbial biomass carbon (Cmic). Detectable soil microbial biomass estimates as revealed by CFI were found after the first rain that occurred following the dry summer period. CFI as well as SIR biomass figures increased during the rainy period to maximum values of 300 ßg Cmic g soil and decreased rapidly toward the end of the rainy season. Under dry soil conditions no reproducible results were obtained for CFI, but SIR figures decreased to 70 μg Cmic g soil during the hot summer period. Soil respiration in the upper 10‐cm soil layer fluctuated significantly on a monthly timescale, whereas the metabolic quotient for CO2 (qCO2) stabilized at low rates only during the rainy season, indicating that microbial activity is rapidly becoming balanced, when climatic conditions allow microbial growth.