Two methods of P. aeruginosa elastase purification are described: Method 1 involves concentration of sample supernatants, followed by DEAE-Sepharose liquid chromatography, whereas Method 2 involves initial fractionations followed by molecular sieving and hydrophobic interaction high-performance liquid chromatography. The choice of methods depends on the available equipment and supplies. The methods of assaying elastase activity described as useful for a variety of applications. The elastin-nutrient agar plate method is a qualitative assay to determine the presence of elastase activity produced by a given culture or colony. Use of the quantitative elastin-Congo red assay is appropriate for determining elastase activities of mid-to-high elastase-producing cultures. For more sensitive determinations of P. aeruginosa elastase activity, use of the fluorogenic substrate is advisable.