A recently described technique, 'Chemical Genetics' unknown sequence amplification method, which requires only one specific oligonucleotide, has broadened the applicability of the polymerase chain reaction to DNA of unknown sequence. We have adapted this technique to the study of the genome of Chlamydia trachomatis, an obligate intracellular bacterium, and describe modifications that significantly improve the utility of this approach. These techniques allow for rapid genomic analysis entirely in vitro, using DNA of limited quantity or purity.