The rate of O2 consumption of a number of Caribbean corals was determined in darkness and the results expressed on a unit-weight and unit-surface-area basis to enable inter- and intraspecific comparisons to be made. Intraspecific comparisons of Montastrea annularis and M. cavernosa and comparisons between species of Agaricia show that corals living in deep water (40 m) have lower rates of respiration than shallow-water corals. Corals such as Acropora and Agaricia, with a high surface-to-volume ratio have higher rates of respiration per unit weight than the massive corals like Montastrea. Differences in rate of respiration are probably the result of differences in energy expenditure in the biosynthesis of tissue growth, and this is determined to a large extent by the nutritional input into the colony from the zooxanthellae.