Three plasmid-mediated chloramphenicol acetyltransferases isolated from different Haemophilus influenzae strains were purified and characterized. All three enzymes had properties in common with the gram-negative family of chloramphenicol acetyltransferase. The Haemophilus enzymes and the enteric type II enzyme were sensitive to 5,5'-dithiobis(2-nitrobenzoic acid), gave the same elution patterns from a highly substituted resin containing a bound chloramphenicol base, and had similar reactions to antisera. All four differed from each other in subunit molecular weight, enzyme activity, and partial protein digestion patterns. The data suggest that the three Haemophilus enzymes belong to the less common type II group and are related, but is not identical, to each other and to the enteric type II enzyme.