Antibody responses to Aeromonas salmonicida A-layer were analysed in family material of Atlantic salmon (Salmo salar), consisting of 791 fish belonging to 34 full-sib groups within 12 paternal half-sib groups. The fish were immunized twice and blood samples were collected three times. Significant increase in antibody titre from first to second, and from second to third sampling, was observed. Genetic variation in antibody titres was observed at the three samplings with estimated heritabilities ranging from 0.16 to 0.20, and a significant heritability estimate was recorded in the antibody response after the second immunization (h2 = 0.16). Moderate to high genetic (r = 0.5-0.72) and phenotypic (r = 0.29-0.57) correlations were found between the titre values at different samplings, and between selected titres and titre increases. Production parameters, such as mean slaughter weight and mean survival rate were obtained for fish which were reared commercially in the sea, and which belonged to the same full-sib groups as those analysed for A. salmonicida A-layer antibodies. No significant correlation between the mean antibody titre to A. salmonicida A-layer in this study and mean slaughter weight and survival rate in full-sib family material in the sea was observed.