The effects of water masses and depth on the distribution of planktic foraminifera across the island slope of southwestern Puerto Rico were studied in Holocene surface sediments. Samples from the depth range of 432–4700 m covered 0.5–95 km distance from the shelfbreak. Shallower samples in this region are altered by winnowing. Plankton net tows through the upper 120 m of the water column sampled the living planktic foraminiferal population in the same area. They contained shallow water benthic foraminifera that were probably brought into suspension on the shelf and transported seawards with the shelf outflow water, illustrating the exchange of water and suspended particles from the shelf to the slope. The grain size spectrum of the sediment samples shows no depth-related trend. The sand fraction (>63 μm) consists of foraminifera, pteropoda and, on the upper slope, of reef detritus. The bulk carbonate content varies from 51 to 73%. The abundance of planktic foraminifera per gram sediment increases with depth, while the number of benthic foraminifera decreases with water depth. The composition of the benthic assemblage shows an increase of the ratio of agglutinated versus calcareous perforate forms. The planktic foraminiferal assemblage (>150 μm) is dominated by Globigerinoides ruber and shows no obvious trend over the sampled depth range. The plankton/benthos ratio increases with depth from 0.63 to 0.99 as a result of opposite trends in accumulation rates of benthic and planktic foraminifera. Accumulation rates of planktic foraminifera increase with distance from the shelfbreak and with water depth from 10,000 to 30,000 specimens cm-2 ka, indicating the influence of ecological and/or depositional processes on their distribution. It is suggested that the tests of planktic foraminifera are displaced in a seaward direction by lateral advection. Therefore, their place of deposition does not lie directly underneath the place of production.