Drying of marine sediment samples is required to determine the number of foraminifers per g as an indication for paleoenvironmental changes. Our results show that oven-drying may lead to alteration of the stable oxygen isotope signal. The delta 18 O values of Turborotalita quinqueloba (Natland) from dried samples are as much as 2.8 per mil lighter than their equivalent from samples which were not dried before preparing. Differences in the isotopic composition of Bulimina aculeata (d'Orbigny) were less dramatic (<0.5 per mil). The drying as well altered the composition of benthic assemblages, thus oven-drying should be generally avoided.