Blood samples of nineteen sea bass from a naturally infected cultured population were analysed in order to evaluate specific antibody response against the parasitic dinoflagellate Amyloodinium ocellatum. The specific antibody response was evaluated by an indirect enzyme-linked immunosorbent assay (ELISA), using whole parasite crude antigen and rabbit IgG anti sea bass-IgM. Experimental data showed that some of sampled specimens developed an adaptive immunological response against the parasite, detectable by indirect ELISA. Results let to conjecture that sea bass, showing an acquired immunity against A. ocellatum, could develop a partial resistance against new infections of the dinoflagellate.