Biometrical analyses were performed on nearly 3200 specimens of distinct coccolith species from the time-series station ESTOC (European Station for Time-series in the Ocean, Canary Islands). Originally begun for calculation of modern species-specific carbonate fluxes, this study was further intensified, both to improve our knowledge of the morphological variability for each of the investigated species, and to check the seasonal size-variations of the various species. Besides the dominant taxa Emiliania huxleyi and Florisphaera profunda, intensive measurements of various parameters have been made on Calcidiscus leptoporus, Gephyrocapsa spp., Helicosphaera carteri, Syracosphaera pulchra, and Umbilicosphaera sibogae. Generally, the species are unimodally distributed, with respect to length/diameter, and show only slight seasonal variation.