In the 20th century, acid rain is believed to have caused significant losses of labile calcium (Ca) from already acidic forest soils in the Northeastern U.S.  At the Hubbard Brook Experimental Forest, in New Hampshire, it has been estimated that as much as half of the labile Ca was lost from the soil.  We added wollastonite (CaSiO3) to a gaged 11.8-ha watershed to restore the base saturation of the soil to pre-acidification levels.  Interestingly, while this treatment increased soil pH, it had no effect on soil microbial N and C cycling.  In this poster, we present the results of quarterly monitoring of soil microbial biomass C and N, net N mineralization, C respiration, and potential net nitrification in the treated and control watersheds.  We also present initial results of experiments designed to test three hypotheses for the lack of a treatment response: (1) microbial biomass and activity in acid forest soils is not pH dependent; (2) the response of microbes to increased soil pH is limited by low phosphorus availability; and (3) Ca-binding makes labile C inaccessible to microbes.