A disadvantage of genotyping bacterial strains by pulsed-field gel electrophoresis is that the procedure requires up to 6 days to complete. We modified a standard pulsed-field gel electrophoresis method (B.E. Murray, K.V. Singh, J.D. Health, B.R. Sharma, and G.M. Weinstock, J.Clin. Microbiol. 28:2059-2063, 1990) so that it could be completed in less than 3 days. We successfully applied this method to the analysis of a variety of gram-positive and gram-negative bacteria.