Histopathological observations in cultured turbot (Scophthalmus maximus L.) larvae are described in varying developmental stages. No striking changes were found during the endogenous feeding period. Alter the introduction of live food, the main lesions encountered were atrophy and degeneration of the digestive system, but these lesions were not associated with high mortality rates in the culture system during the early stages. Subsequently, during the stages of organogenesis, progressive bacterial colonization of the digestive tract was observed, accompanied by severe enteritis, especially in the more mature larvae. High mortality rates were detected in the rearing system at this time. In severe cases, necrosis of pancreatic acini and hepatocytes were observed also. Swimbladder alterations such as non-inflation, malformation and bacterial invasion via the pneumatic cluct were frequently observed at all stages oh development. It is suggested that infectious agents may play an important role in the high mortality often encountered in cultured turbot larvae. © 1993, Academic Press Limited. All rights reserved.