Studies of the bathymetric distribution of planktonic Foraminifera indicate that they are most abundant in the euphotic zone of the oceanic waters around Bermuda. Seasonal fluctuations in the relative and absolute abundances of 15 species have been observed from 106 plankton samples, showing a regular succession in the foraminiferal populations. Globorotalia hirsuta, G. truncatulinoides, Globigerina inflata, and G. bulloides were most abundant in winter and spring, when temperatures within the euphotic zone ranged between 18 degrees and 23 degrees C. and salinities varied between 34.40%. and 36.60%. Globorotalia menardii, Globigerinoides sacculifer, and G. conglobatus reached their maximum concentrations in summer and fall, when temperatures ranged between 23 degrees and 27 degrees C. and salinities between 36.10% and 36.40%. The oceanographic and paleoecologic implications of these observations are discussed for the northern Sargasso Sea.