ABSTRACT: The distribution of yellow-head virus (YHV) in 9 different tissues and organs including the branchial portion of the gill, nerve cord, lymphoid organ (Oka), heart, midgut, hepatopancreas, head soft tissues (HST), abdominal muscle, and eyestalk of experimentally infected moribund white shrimp Penaeus vannamei (Boone) was examined by bioassay using penaeid shrimp indicators and by quantal assay (TCID₅₀) in primary shrimp Oka organ cell cultures. Infectious YHV was demonstrated in all the tissues and organs tested; inoculation of each of the tissue and organ filtrates into experimental shrimp resulted in 100% mortality within 6 to 9 d postinfection. The TCID₅₀ assay in primary Oka organ cells revealed that Oka, gill and HST contained 10- to 800-fold higher titers of YHV than the other tissues and organs tested and suggested that they are apparently the primary target tissues and organs for YHV infection.