Josef et al. (this volume) found no measurable microbial enhancement of olivine dissolution rate as measured using dissolved Li and Si for as long as 709 days. It had been hypothesized that microbes might mediate reaction of olivine with water, capitalizing on the chemical potential energy inherent in the disequilibrium between mantle olivine and surface waters. If so, microbial activity might enhance olivine dissolution rates. Moeseneder et al. (unpubl. data) inoculated sterile basalt glass and sterile olivine with bacteria cultured from pillow lavas and observed an enhancement in dissolution rates via high Li and Si in solution, compared to sterile controls. Josef et al. (this volume) did not culture microorganisms from Leg 209 peridotite samples, so the presence of microbial matter in these samples is not certain. Thus, the lack of enhancement of dissolved Li and Si in their samples, compared to sterilized controls, could be due to a variety of factors including a lack of living microbes in the samples.