Eleven strains of Alcaligenes denitrificans subsp. xylosoxydans produced a beta-lactamase with a pI of 5.7 with kinetic data characteristic of a PSE-1-type enzyme. A CARB-type enzyme was identified by using an intragenic DNA probe of blaCARB. Hybridization of genomic DNA after XbaI restriction and pulsed-field electrophoresis suggested a chromosomal location for the gene.