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Previous studies on the effect of pulsed electric fields of ten's of microsecond duration on bacteria have shown that the lethality increases less with pulse duration than with electric field strength. Consequently, it should be possible to minimize the required energy for debacterialization by applying shorter pulses with higher electric fields. Experimental studies of the effects of 60 ns, 300 ns and 2 /spl mu/s electric field pulses on the viability of E. Coli have confirmed this hypothesis. The experimental observations indicate also that lysing of bacteria for nanosecond pulse durations may be due to damage of the cell interior rather than the cell membrane. The effect of electric field pulses on more complex organisms was studied using marine crustaceans. It could be shown that for a certain pulse duration the required energy for stunning or killing is minimum. The observed dependence of micro-organism lethality or temporary damage on field strength and pulse duration allows us to improve the energy efficiency of systems which make use of the effect. Examples are sterilizers (e.g. for drinking water) and electrical filters for the prevention of biofouling in cooling systems.