The effect of tidal currents on the upwelling in the Messina Straits was investigated during summer 1992, both by continuous survey of tracer parameters with a sailing vessel and by 24-hour surveys at significant hydrological stations. The current field of the Straits was also monitored by a grid of currentmetric chains and periodical surveys using a Doppler current profiler. Deep waters reach the upper layer everywhere in the Ionian basin of the Straits during syzygy, with the exception of the middle zone of the system where the warmer Tyrrhenian surface water flows. The upwelling of nutrients stimulates phytoplanktonic growth and greatly increases the primary productivity. Divergence of deep waters is strongly reduced in quadrature phase, when current velocity is attenuated. The oscillation of the tidal level is mainly responsible for the upwelling at the sill, while the vertical movement induced by longitudinal advection on the lateral areas appears to be correlated with the speed of both southward and northward fluxes.