Specific-pathogen-free (SPF) chickens were infected with infectious bursal disease virus (IBDV) serotype II (turkey, Missouri isolate) at 1 day or 4 weeks of age. Chickens infected at 1 day had small bursas 3 weeks postinfection (PI). Bursas were necrotic and inflamed through 1 week PI. Post-necrotic atrophy of the bursas was marked at 3 weeks PI, and plasma cells in the Harderian gland were depleted. Chickens infected at 4 weeks had slightly enlarged spleens with small gray foci on the surface at 1 week PI. The bursas had massive necrosis and hemorrhages on the mucosal surface and had gelatinous yellowish transudate covering the serosal surface; some bursas were gray. Bursas were smaller than normal through the end of the experiment (4 1/2 weeks PI). At 1 week PI, histologic lesions were multifocal lymphoid necrosis of spleens and necrotic inflammation of the bursas. Post-necrotic atrophy of the bursas was found 2 weeks PI through the end of the experiment. Compared with uninfected controls, infected chickens had significantly more pyroninophilic blast cells in the spleen at 1 week PI and the bursas at 4 1/2 weeks PI. Plasma cells in the Harderian glands of this infected group were depleted as well.