For selective isolation of Pseudomonas aeruginosa from clinical samples. CETRIMIDE AGAR BASE (VEG.) isused for the selective isolation of Pseudomonas aeruginosa. The medium contains quaternary ammonium, cationic detergent compound like Cetrimide which has a property to inhibit all the bacteria except P. aeruginosa thus making the medium selective for Pseudomonasaeruginosa. Veg. gelatin digest provide the nitrogen and carbon sources. Cetrimide causes release of nitrogen and phosphorus from bacterial cells other than P. aeruginosa. Agar is solidifying agent. Magnesium chloride and potassium sulphate stimulates the bacterium to produce and secrete a pigment called pyocyanin due to which the colony colour turns light green, and also they forms a grape like odour due to production of aminoacetophenone. These are the typical characteristics that help isolating P.aeruginosa using cetrimide agar base. On incubation of plates in an inverted position (agar side up) at 35 ± 2°C for 18-48 hours of P. aeruginosa showed profuse growth whereas strain of E.coli inhibits the growth in this medium. If the cfu/ml is high then the test sample can be directly inoculated onto this cetrimide medium.