Cefoxitin resistance in Klebsiella pneumoniae and Escherichia coli strains isolated in Greek hospitals was found to be due to the acquisition of similar plasmids coding for group 1 beta-lactamases. The plasmids were not self-transferable but were mobilized by conjugative plasmids. These elements have also been spread to Enterobacter aerogenes, The most common enzyme was a Citrobacter freundii-derived cephalosporinase (LAT-2) which differed from LAT-1 by three amino acids.