The aim of this study was to examine the influence of pH, water activity (aw) and temperature on the killing effect of pulsed electric fields (PEF). Escherichia coli and Saccharomyces cerevisiae suspended in a model media were subjected to 20 pulses with 4 ?s duration in a continuous PEF system, during which the effects of pH (4.0-7.0), aw (1.00-0.94) and inlet temperature (10°C and 30°C) could easily be studied. Electrical field strengths were set to 25 kV/cm for S. cerevisiae and 30 kV/cm for E. coli and the highest outlet temperature was monitored to 44°C. A synergy of low pH values, high temperatures and PEF processing was observed. A drop in pH value from 7.0 to 4.0 resulted in the reduction of E. coli by four additional log units, whereas for S. cerevisiae, the pH effect was less pronounced. Lowering aw seems to protect both E. coli and S. cerevisiae from PEF processing. © 2001 Elsevier Science Ltd.