A high frequency of recombination has been shown to occur during replication of the coronavirus mouse hepatitis virus (MHV) in vitro as well as in vivo. Although sequencing of field strains of coronavirus infectious bronchitis virus (IBV) has indicated that IBV strains also undergo recombination, there has been no experimental evidence to support this deduction. To investigate whether recombination occurs in IBV, embryonated eggs were coinfected with IBV-Beaudette and IBV-M41. Potential recombinants were detected by strain-specific polymerase chain reaction (PCR) amplifications, using oligonucleotides corresponding to regions in the 3' end of the genome. Sequencing of the PCR products confirmed that a number of recombinations had occurred between the two strains.