ABSTRACT: A numerical model is proposed for investigating the potential of calcium carbonate dissolution in copepod guts. A sensitivity analysis is performed to reveal critical parameters. Gut pH sets the dissolution rate and gut-clearance rate determinesthe time scale on which ingested calcite is subject to dissolution. Highest dissolution is obtained when the individual zooplankton is alternating between grazing and non-grazing and feeding is restricted to the night-time period. Model results show thatup to 70% of the ingested carbonate may be dissolved in the guts, considering reingestion of faecal pellets in the absence of a phytoplankton bloom, while ~15% dissolution is to be expected in a bloom situation. An estimate is made for the contributionof calcite dissolution in copepod guts to the proposed global calcite loss in the water column.