A genome wide search in European Wild Boar x Swedish Yorkshire (W x Y) inter-cross pigs has earlier identified quantitative trait loci (QTL) for leucocyte number and function on porcine chromosomes 1 and 8 (SSC 1 and 8). To verify the involvement of these chromosomal regions in the regulation of haematocrit (Hem) and haemoglobin (Hb) levels, leucocyte numbers and in vitro leukocyte functions (mitogen induced proliferation and IL-2 production, virus induced interferon-alpha production and neutrophil phagocytosis), animals of different genetic backgrounds were analysed. The animals comprised a back-cross sire family (n=47) of W x Y pigs and six crossbred [Y x Landrace (L)] sire families (n=191). They were genotyped for 16 genetic markers and an interval analysis was performed. On SSC1, a QTL close to S0082 on the q-arm that influenced numbers of white blood cells in L x Y pigs and numbers of band neutrophils and CD8(+) cells in W x Y pigs was identified (P<or=0.01). An additional SSC1 QTL was identified on the p-arm close to S0008 with influence on numbers of CD2(+) cells in W x Y pigs (P<or=0.05). On SSC8, a QTL influencing Hb (P<or=0.01) and Hem (P<or=0.05) levels was identified close to KIT in the W x Y pigs. For L x Y pigs, a second QTL, distal to KIT and close to S0069, on SSC8 influenced the numbers of MHCII(+) cells and mitogen induced proliferation (P<or=0.05), whilst the QTL close to KIT influenced the number of IgM(+) cells in these pigs (P<or=0.05). The results confirm the involvement of earlier identified regions of SSC1 and SSC8 on porcine immune parameters and some candidate genes were suggested.