Pyrene has been reported as one of the most important polycyclic aromatic hydrocarbons (PAHs) found as environmental contaminant in estuaries and coastal areas. Therefore, in the present study, the acute effects (96h) of pyrene on the common goby Pomatoschistus microps, a key species in several European estuaries and lagoons, were assessed through individual exposure of juveniles to 0.125, 0.25, 0.5 or 1mgL−1 of pyrene. Mortality, swimming performance and several biomarkers were used as effect criteria. The 96h median lethal concentration (LC50) was 0.871mgL−1 and the swimming performance of fish was significantly decreased at all the pyrene concentrations tested. A significant increase of bile metabolites was found at increasing concentrations of pyrene (LOEC=0.125mgL−1) indicating the production of metabolites during the biotransformation of the toxicant. Pyrene significantly inhibited the activity of head acetylcholinesterase at 0.5mgL−1 and muscle cholinesterases at 1mgL−1. A bell-shape pattern response in the activity of muscle lactate dehydrogenase and isocitrate dehydrogenase (IDH) was found, with a significant increase of IDH at 0.25mgL−1, suggesting changes in the pathways of energy production. A bell-shape response for the antioxidant enzyme glutathione peroxidase and a less evident bell-shape response of glutathione S-transferase and glutathione reductase were also found. Lipid peroxidative damage was found in liver (0.25mgL−1) and gills (0.50mgL−1). It should be noted that although the concentrations of pyrene tested in the present study are higher than those that have been found in estuarine water and sediments, the occurrence of pyrene as single environmental contaminant is rare; in fact, the most common situation is the contamination by several PAHs, a considerable part of them sharing toxicological properties with pyrene and thus with a high probability of inducing additive or synergistic effects in simultaneous exposures. The findings of the present study are ecologically relevant and should be taken into consideration in the management of estuaries contaminated by petrochemical products. Moreover, effects of pyrene in this species should be further investigated.