Feeding, respiration, and excretion rates (ammonium and phosphate) of mesozooplankton from the equatorial Pacific upper water column (0--100 m) were measured along the 180th meridian at different stations between 8¿S and 8¿N, and more repeatedly, at two time series stations, located at 3¿S (TSS1) and the equator (TSS2). Only particles of size >8 ¿m were grazed by the organisms used for the experiments. Grazing rates were higher at TSS1. Ammonium excretion was also maximum at TSS2, resulting in lower O/N values. This suggests that food particles were richer in terms of protein content at the equator, as is also indicated by the lower C/N ratio of particles and the higher proportion of heterotrophic protozoans. Some variations in mesozooplankton specific composition (more carnivorous copepods being present in the equatorial samples) could also explain these O/N differences. Diel variations were observed. Significantly higher grazing, respiration (only at TSS1), and excretion rates were recorded during the day, suggesting that feeding activity was related to the daytime increase of primary production. Using the grazing rates determined under experimental conditions, the grazing pressure on the stock of food particles >8 ¿m was very low (8-¿m food particles would reach 14% of the standing stock d-1.