Abstract: A cocaine esterase has been isolated from a strain of the bacteria Pseudomonas maltophilta, The cocaine esterase catalyses the debenzoylation of cocaine, This reaction may be used in the detection of cocaine. The enzyme may be incorporated into sensors for this purpose. The cocaine esterase is preferably obtainable from Pseudomonas sp. NCIMB 40427. It catalyzes the debenzoylation of cocaine, has a molecular weight in the unaggregated form of about 120,000 daltons as determined by gel filtration, has esterase activity specifically at the benzoate ester linkage of cocaine, separates at a major band of Rf about 0.2 on PAGE in its aggregated form, and it is completely inhibited by 1 mM phenylmethylsulphonyl fluoride but ineffectively inhibited by 1 mM eserine, each determined at 30.degree. C. with respect to 2 mM cocaine as substrate.