Laboratory-reared larvae of mussels (Mytilus galloprovincialis ) were incubated with and without sediment in a novel turbulence-producing machine. The sediments used were fine silt from the Gironde Estuary and from the German Wadden Sea. Larvae incubated in turbulence without sediment, and in suspended sediment concentrations similar to in situ conditions had growth rates which did not vary significantly from those of the controls. The growth rates of larvae incubated in 5 to 20 g/l of sediment were reduced by 20 to 50%. Survival was lower in larvae incubated with sediments than in turbulent and non-turbulent controls, but it was not correlated with sediment concentration. The results indicate that the mechanical effects of turbulence and turbidity on mussel larvae are minor.