The effect of elevated atmospheric CO2 concentration (Ca) on soil carbon and nitrogen accumulation and soil microbial biomass and activity in a native Florida scrub oak community was studied. The plant community, dominated by Quercus myrtifolia Willd. and Q. geminata Small, was exposed for 2 years to elevated Ca in open-top chambers. Buried subsoil bags were retrieved after 1 year of exposure to elevated Ca. In addition, soil cores were taken twice from the chambers within two weeks in July 1998 (the first after a long dry spell and the second after 25 mm of rainfall) and divided into rhizosphere and bulk soil. Soil organic matter accumulation (excluding roots) into the buried subsoil bags was lower in elevated than in ambient Ca. Concentrations of soluble carbon and ninhydrin-reactive nitrogen (Nninh) in the rhizosphere soil were reduced by elevated Ca for the first sampling date and unaffected for the second sampling date. Microbial activity, measured as fluorescein diacetate (FDA) hydrolysis, decreased in elevated Ca for the first sampling date. Microbial biomass carbon and nitrogen in the bulk soil were unaffected by elevated Ca. There was no effect of elevated Ca on bacterial numbers in the rhizosphere.