A strain of T. maritimum (89/4762) isolated from diseased Atlantic salmon was grown in an aerated 10-l carboy using Shieh's medium formulated with filtered (0.22 μm), sterilised natural seawater (35 ppt). The medium was heat sterilised at 121 °C for 40 min to achieve adequate heat penetration in the volume of medium. The bacteria were grown in 5-l of broth at room temperature (20 °C) with aeration (120 l/h) and harvested after 48 h incubation. Cell con- centration reached a mean of 1.27 × 109 cells/ml as determined by direct counts using a Helber counting chamber. The bacteria were inactivated by the addition of formalin (37–38% w/w formaldehyde) to a final concentration of 5 ml/l. After 48 h refrigeration, the cells were collected by centrifugation at 3000 ×g for 30 min and washed three times using phosphate buffered saline (PBS, pH 7.4). Cells were resuspended in PBS to a final concentration of 1.08 × 1010 cells/ml and formalin (37–38% w/w formaldehyde) added to a final concentration of 0.1% v/v as a preservative. A vaccine preparation containing Freund's incomplete adjuvant (FIA) (Sigma) was also prepared. The adjuvant was mixed 50:50 with the vaccine suspension just prior to use. A 2 ml syringe with a 23 gauge needle was used to aspirate the preparation until a stable emulsion had been formed. Both vaccine preparations used for this study contained approximately 1.79 × 109 cells/0.1 ml inoculum.