Five chicken lines were experimentally infected with a HPAI H7N1 virus, to examine the variation in susceptibility to infection. Three lines showed high susceptibility to the virus, while two showed some resistance, with 7 out of 20, and 11 out of 15 birds, respectively, remaining healthy and surviving the experimental infection. Genotyping for the G/A polymorphism at position 2032 of Mx cDNA showed that one line was fixed for the G allele, and two were segregating for A and G alleles. Birds in the other two lines were selected to be fixed for the A allele. Statistical analyses indicated that the Mx genotype did not affect the clinical status or the time course of infection after viral inoculation.