Oxygen consumption and excretion rates for ammonia and soluble reactive phosphorus (SRP) by mesozooplankton were studied at a series of stations located along a transect between the islands of Mallorca and Menorca during July 1983. As in a previous cruise also made during the summer stratification period (July 1982), vertical profiles of zooplankton biomass showed the existence of a zooplankton maximum, coinciding with the chlorophyll, phytoplankton and super(14)C fixation maxima. The mean zooplankton excretion in the epiplankton layer can provide 13.7-16.8% of the N (as ammonia) and 67.2-76.6% of the P (as SRP) requirements for primary production, assuming a mean carbon-to-nitrogen assimilation ratio (C/N) of 6.65, equal to the mean C/N ratio of the particulate matter in the cruise, and a C/P assimilation ratio of 183.7 (equivalent to the mean composition ratio of phytoplankton).