Aim: To develop a liquid formulation of Pseudoxanthomonas sp. RN402 for prolonged storage and maintaining high survival rates and pyrene biodegradability. Methods and Results: Liquid formulations of RN402, designated as L-RN402, were prepared by suspending bacterial cells (10(9) CFU ml(-1)) in various buffers. Analysis found that phosphate buffer containing glycerol maintained high survival rate (94%) as well as pyrene biodegradability of bacteria after a 30-day storage. This L-RN402 could be stored at 30 degrees C for at least 6 months. Bioaugmentation treatment with stored L-RN402 resulted in the complete degradation of pyrene (300 mg kg(-1)) in soil microcosms within 4 weeks. RN402 could be detected by denaturing gradient gel electrophoresis throughout the period; moreover, real-time PCR indicated the presence of high number of nidA-containing bacteria. Conclusions: A liquid formulation of RN402, an effective pyrene degrader, was developed by suspending RN402 in phosphate buffer containing 1% glycerol. This formulation could be stored at 30 degrees C for at least 6 months and maintain high efficacy in the treatment of pyrene-contaminated soil. Significance and Impact of the Study: This work is the first description of a liquid formulation of pyrene-degrading bacteria for prolonged storage that retains biological activity for the treatment of environmental pollutants.