Publisher Summary This chapter describes the Baird–Parker liquid (LBP) medium modification of Baird–Parker's agar, which allows the selective enrichment of small numbers of injured cells of Staphylococcus aureus. Selectivity is attained through the addition of potassium tellurite and lithium chloride, while sodium pyruvate enhances productivity, especially the recovery of stressed cells. Anaerobic incubation of the medium reduces the likelihood of false positive results from micrococci, a common isolate on Baird–Parker agar. The medium is used for the isolation of Staphylococcus aureus from pharmaceutical products, where small populations of stressed cells may be of significance. LBP is composed of peptone, pancreatic digest of casein, beef extract, yeast extract, sodium pyruvate, glycine, lithium chloride, potassium tellurite, and distilled or deionized water. The chapter also describes the preparation of LBP. All the ingredients are dissolved except the potassium tellurite in the water with the aid of heat. Cool to room temperature and adjust the pH to 6.6. Dispensed into test tubes and sterilize at 121° C for 15 minutes. When cooled to approximately 50° C, add filter sterilized potassium tellurite solution to give a final concentration of 100 μg/ml. After removal of agar or paraffin plug subculture, all tubes show growth, whether or not they show a black precipitate, by streaking a loopful of culture to Baird–Parker agar. Agar plates are incubated and examined as detailed in the monograph on Baird–Parker agar.