Catecholamines are pivotal signal molecules in the neuroendocrine-immune regulatory network, and implicated in the modulation of immune response. In the present study, the activities of some immunerelated enzymes and the concentration of catecholamines were determined in circulating haemolymph of scallops Chlamys farreri after bacteria Vibrio anguillarum challenge. The activities of superoxide dismutase (SOD), catalase (CAT) and lysozyme (LYZ) increased significantly and reached 610 U mg1 at 12 h, 37.6 U mg1 at 6 h and 261.5 U mg1 at 6 h after bacteria challenge, respectively. The concentration of norepinephrine, epinephrine and dopamine also increased significantly and reached 114.9 ng mL1 at 12 h, 86.9 ng mL1 at 24 h and 480.4 pg mL1 at 12 h after bacteria challenge, respectively. Meanwhile, the activities of these immune-related enzymes in haemolymph were monitored in those scallops which were challenged by bacteria V. anguillarum and stimulated simultaneously with norepinephrine, epinephrine and adrenoceptor antagonist. The injection of norepinephrine and epinephrine repressed significantly the induction of bacteria challenge on the activities of immune-related enzymes, and they were reduced to about half of that in the control groups. The blocking of a and b-adrenoceptor by antagonist only repressed the increase of CAT and LYZ activities significantly, while no significant effect was observed on the increase of SOD activities. The collective results indicated that scallop catecholaminergic neuroendocrine system could be activated by bacteria challenge to release catecholamines after the immune response had been triggered, and the immune response against bacteria challenge could been negatively modulated by norepinephrine, epinephrine, and adrenoceptor antagonist. This information is helpful to further understand the immunomodulation of catecholamines in scallops.