White shrimps, Litopenaeus vannamei, were tested in two indoor trials to determine the effect of fumonisin B1on (i) immune response, (ii) histopathology, and, (iii) muscle proteins. Trial 1: (0, 0.5, 0.75 and 1.0 μg/g of FB1levels, 18-day duration; shrimp 5-6 g) to evaluate the FB1effect on the immune system and histopathology response. Trial 2: (0.0, 0.5, 0.75 and 1.0 μg/g of FB1levels, 16-day duration; shrimp 5-6 g) to detect FB1effect on muscle proteins. Prophenoloxidase activity was affected by all FB1concentrations tested. Both, total haemocyte count and phenoloxidase activity decreased by the 18th day in shrimp exposed to FB1. Marked histological changes in the hepatopancreas of shrimp fed on diet containing FB1, at the all FB1levels tested, as well as a necrotic tissue were observed. Changes in both, electrophoretic patterns and thermodynamic properties of myosin extracted from shrimp exposed to FB1were also observed. © 2008 Elsevier Ltd. All rights reserved.