In order to ensure shrimp aquaculture production, immunology has become a priority in terms of disease control and prevention. Research must be devoted to the identification of anti-infectious effectors at the cellular and molecular levels. In this review, recent results obtained in the shrimp Penaeus japonicus are presented and discussed with reference to the Crustacea and other arthropods. Various cellular and plasma haemolymph components were characterised both antigenically and functionally. Haemocyte subpopulations, separated by isopycnic centrifugation on Percoll were discriminated using two monoclonal antibodies, 40E2 and 40E10. The granular cells were recognised by the antibody 40E2 specific for a plasmatic protein. By comparison, the hyaline and semi-granular cells were recognised by the antibody 40E10, which immunoprecipitated a plasmatic protein identified as an agglutinin. Moreover, an α2-macroglobulin-like protein present both in plasma and in haemocytes was antigenically characterized in P. japonicus as well as a plasma clotting factor. Functional studies have been undertaken by considering antimicrobial effectors and haemocyte-mediated oxidative defence mechanisms studied by chemiluminescence. Prospects on findings in shrimp immunology are discussed with reference to their application to zoosanitary prophylaxis and disease prevention. © 1995 Academic Press Limited.