We investigated here the role of adenine deaminase in Pseudomonas synxantha A3. Adenine deaminase may not be essential for the growth of the organism. Compared the enzyme activities of adenine-deficient mutant with those of parent strain, adenine deaminase which supply hypoxanthine to the cell seems to act on the degradation of adenine rather than on the salvage synthesis of nucleotides. The enzyme appeared to be absent from the periplasm and might be irrelevant to adenine transport. These observations provide an evidence that this enzyme seems to be constitutive enzyme.