The studies on alpha-protease inhibitors systems, controlled by four tightly linked loci, were performed within 159 families of Norwegian Landrace (NL) and 40 families of Czech Landrace (CL) pigs. Significant differences in allele and haplotype frequencies between the two breeds were shown. The SE-F and SSsS haplotypes (Pi1, Po1A, Po1B, Pi2 loci) appeared to be the most frequent haplotypes in NL and CL breeds respectively. This system of blood plasma proteins can be very useful for studying the relationship between breeds.