Deoxyribonucleic acid (DNA) microarrays are widely used for differential expression studies and for detection of virulence genes in pure bacterial cultures. Their use in complex microbial samples, such as soil and wastewater, has been relatively less studied. This report presents the results of a systematic effort to apply DNA microarrays to pathogen detection and to bacterial source tracking (BST) in wastewater. Parameters such as the method of DNA extraction from the samples, the type of immobilized probe (whether polymerase chain reaction [PCR] amplicons or oligonucleotides), the length and method of immobilization of oligonucleotides, the method of DNA labelling, the combination of PCR amplification with microarray hybridization and the choice of PCR targets have been optimized.