Due to the increasing use of pesticides in coastal areas and the exponential growth in production and use of nanoparticles in the last decade, their impact on the environment and marine ecosystems, as well as mechanisms and effects on organisms, remain unresolved and hence a cause for concern. The goal of this study was to investigate the toxicity of coexposure to permethrin and silver nanoparticles in the Mediterranean mussel Mytilus galloprovinicalis. Mussels were treated with silver nanoparticles at concentrations in the range 5-50 μg/L, permethrin concentrations in the range 1-100 μg/L and combinations thereof. Evaluation of toxic effects was determined by SOS test, lysosomal membrane stability and acetylcholinesterase enzyme activity. The results of the SOS test indicate toxic effects of silver nanoparticles with a reduction of mussel survival in air, mussels treated with permethrin showed enhanced survival, while the survival of individuals treated with silver nanoparticle-permethrin combinations did not differ significantly from the control group. The results of tests on stability of lysosomal membranes indicate that silver nanoparticles and permethrin cause reductions in membrane stability with possible synergistic effects in mussels treated with toxicant combinations. Acetylcholinesterase activity increased during 24 h of exposure, while a decrease in exposure was noted after 48 hours. The increased acetylcholinesterase activity may indicate the activation of the organisms' defense mechanisms, with a reduction in activity showing a reduced role of the toxicants, either through aggregation processes which reduce the rate of ionic silver release or sequestration of permethrin by adsorption on nanoparticles.