Chickens representing two different inbred lines (layer and meat-type) and three different B haplotypes (BW1, B19 and B131) were infected with infectious bursal disease virus (IBDV) at 21 days of age. Mortality was recorded, and surviving chickens were killed and examined either 3 or 17 days post-infection. Non-infected control chickens were run in parallel. The variables recorded were all significantly changed by the virus infection, including the serum concentration of mannan-binding lectin that was increased 2-fold 3 days post-infection. A significantly increased mortality, liver to body weight ratio and erythrocyte sedimentation rate (ESR) was seen among chickens from the layer type line compared with the meat-type line. In addition, the haplotype of the chickens influenced the atrophy and hypertrophy of the thymus, It was concluded that the meat-type chicken line was more resistant to IBDV infection than the layer-type line, and that mortality rate, liver to body weight ratio and ESR were valuable variables for evaluation of the level of IBDV infection-induced inflammation and disease.