The combined effect of high hydrostatic pressure processing, addition of nisin and acidification on aerobic mesophilic and psychrotrophic bacterial populations of mechanically recovered poultry meat (MRPM) kept under refrigeration (2°C) was evaluated 1, 15 and 30 days after pressurization. Nisin (0, 12.5, 100 and 200 ppm) and glucono-delta-lactone (GdL; 0 and 1%) were added to MRPM. Vacuum-packaged samples were treated at 350 or 450 MPa and 2°C for 15 min using both continuous pressurization and three-cycle oscillatory pressurization for 5 min per cycle. In some samples a reduction of mesophile counts between 3.44 and 5.38 log cfu g-1 was found. Psychrotrophes seemed to be more sensitive; in samples with 100 ppm of nisin and GdL treated at 450 MPa with cycles they were reduced to undetectable levels (a lethality of approximately 7.5 log units). Cycle pressurization showed slightly better results than continuous pressurization. The combination of 350 MPa, 100 ppm of nisin and 1% of GdL was enough to extend the shelf life of MRPM during the 30 day chilled storage.