Using flow cytometry and leucocyte specific monoclonal antibodies, neutrophils and B-cells were studied in blood and head kidney from wild strains of Atlantic salmon. The strains were Vosso and Blege, being an anadromous and landlocked strain, respectively. Smoltification was induced using a simulated natural photoperiod and sampling was performed monthly for 6 months and ended for the Blege strain at the time of seawater transfer while samples were collected from the Vosso strain after 4 weeks in seawater. Throughout the observation period, the mean proportions of neutrophils in both head kidney leucocytes (HKL) and peripheral blood leucocytes (PBL), were highest for the Vosso strain. The opposite was observed for B-cells where the Blege strain had higher or similar mean proportions compared to the Vosso strain. There were some differences between HKL and PBL. The mean proportion of neutrophils was always higher in HKL than in PBL and the mean proportion of B-cells was higher in PBL than in HKL. The fluctuations during the observation period, in the proportions of B-cells and neutrophils of the analysed cell population, showed mainly the same pattern in both strains. Differences between the strains were observed at various times in the mean of total number of leucocytes per gram head kidney and per millilitre of blood. The fluctuations throughout the experimental period in total numbers of leucocytes in head kidney and blood followed mainly the same pattern in both strains. The results of the leucocyte analyses suggest that there are differences between the anadromous and landlocked strains with respect to what cell type is present in highest proportion in the leucocyte samples from head kidney and blood. The striking similarity between the strains is the profiles of proportions of B-cells and neutrophils in HKL and PBL during the smoltification period.