Xanthomonas albilineans, the causal agent of leaf scald disease, produces the phytotoxin, albicidin, which interferes with DNA replication in chloroplasts resulting in chlorosis of affected plant tissues. Albicidin is produced by all naturally occurring strains of X. albilineans and is unique to the pathogen; thus, the genes involved in albicidin production might provide a suitable target for a PCR-based diagnostic assay for leaf scald disease. We have cloned DNA fragments which complement albicidin production in isolates of the bacterium where albicidin production has been blocked by Tn5 mutagenesis. For development of PCR primers, an 832 bp subclone of one of these cloned DNA fragments was sequenced. Computer programs were then used to select candidate primer pairs from the sequence and evaluate their exclusivity with respect to other known DNA sequences. Two 19 base oligonucleotides were selected for further study as primers and commercially synthesized. In preliminary PCR tests with the oligonucleotides primers, the expected 664 bp DNA product was obtained for all five strains of the pathogen tested. The strains were.representative of the two genetic types of X. albilineans presently known to occur in Florida.