A polymerase chain reaction (PCR) assay was developed for the detection of avian leukosis virus strain J (ALV-J) in chickens. Primers were based in the E element and the 3' terminus of the long terminal repeat of proviral ALV-J. PCR products were amplified from genomic DNA extracted from chicken embryo fibroblasts (CEF) infected with either strain HPRS-103, the prototype of ALV-J, or field isolates of ALV-J obtained from broiler breeder flocks in the United States that exhibited myeloid leukosis. The newly developed PCR detected ALV-J in DNA prepared from CEF inoculated with ALV-J but not from CEF inoculated with subgroup A, B, C, D, or E. The PCR also detected ALV-J in DNA prepared from blood, combs, and toes obtained from chickens experimentally infected with ALV-J and in DNA obtained from peripheral blood monocytes from naturally infected broiler breeder chickens. The PCR described here offers a specific and sensitive alternative to conventional virus isolation tests for ALV-J.