In vitro antigen specific responsiveness of trout leucocytes was monitored over time, following immunisation with three Aeromonas salmonicida vaccine preparations; strain MT004 in saline (MT004/PBS), strain MT004 grown under iron restricted conditions using AlOH as adjuvant (MT004/AlOH), and the commercially available vaccine Furogen. Saline injected fish served as controls. While antigen specific responses in A. salmonicida injected groups were higher than controls, antigen specific proliferation, MAF production and antibody production were all highest in leucocytes elicited from Furogen injected fish. MT004/PBS immunised fish were ranked second and MT004/ AlOH fish ranked third, with only their antibody response being significantly above control values. Thus, the influence of vaccine treatment was seen to have a similar effect on each antigen specific parameter assessed. Antibody production against MT004 from individual fish was seen to correlate with both their relative proliferation and MAF secretion to this antigen, which also correlated with one another. The potential of such antigen specific in vitro correlates of immunity to aid vaccine design are discussed.