We report δ13C and δ18O values for Rose Bengal-stained benthic foraminifera from a set of box cores from continental margin environments in the Atlantic and Pacific oceans. These isotopic results are compared with foraminiferal distribution data and pore water δ13C profiles to evaluate the importance of environmental (microhabitat) effects on the carbon isotopic composition of benthic foraminifera. The δ13C values of infaunal taxa are consistently lower than those of epifaunal taxa, suggesting that microhabitat effects on test composition do exist. The δ13C differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the δ18O differences between benthic foraminifera tests and equilibrium calcite, but they do correlate with variations in the chemistry of sediment pore waters. However, interspecific δ18O differences as well as δ13C differences between species with similar vertical distributions in the sediments indicate that taxon-specific “vital” effects also influence test composition.