Abstract Laboratory cultures of several species of benthic foraminifera were grown under controlled physical and chemical conditions during months-long experiments carried out at the University of South Carolina in 2001 and 2002. A dozen experimental culture chambers contained a c . 1–3 mm layer of trace-metal free silica substrate, and were continuously flushed with water from a large (1600 L) seawater reservoir with known, constant temperature and composition (δ 18 O(water), carbonate system chemistry, and trace element concentrations). Each year, in most of the culture chambers, one or more species reproduced, producing hundreds of juveniles which grew into size classes ranging from 100 to 500 microns. Bulimina aculeata was the most successful species in the 2001 cultures, and both B. aculeata and Rosalina vilardeboana were abundant in 2002. We determined the shell C and O isotopic composition of the cultured foraminifera, and compared these isotopic values with the water chemistry of the culture chambers, and also with the shell chemistry of field specimens collected from sites on the North Carolina and South Carolina (USA) continental margin. The cultured foraminifera showed substantial offsets from the δ 13 C of system water dissolved inorganic carbon (−0.5 to −2.5‰, depending on species) and smaller offsets (0 to −0.5‰) from the predicted δ 18 O of calcite in equilibrium with the culture system water at the growth temperature. These offsets reflect at least three factors: species-dependent vital effects; ontogenetic variations in shell chemistry; and the aqueous carbonate chemistry ([CO 3 − ] or pH) of the experimental system.