PCR is a quick and effective way of identifying the presence and 'affiliation' of bacteriophages, or phage-encoded genes from environmental samples, bacterial cells or purified viruses. The limitations are that you have to know what you are looking for in order to find it. Although the bacteriophage world does not have the advantage of a conserved gene, present in all members, there are many phage genes that do show nucleotide conservation even between phages which infect fairly divergent taxa. As more sequence data become available through both metagenomic approaches and the sequencing of complete bacteriophage genomes, PCR primers can be further refined and thus it should be an increasingly useful tool for bacteriophage biology.