Pseudomonas sp. strain ADP initiates atrazine catabolism via three enzymatic steps, encoded by atzA, -B, and -C, which yield cyanuric acid, a nitrogen source for many bacteria. In-well lysis, Southern hybridization, and plasmid transfer studies indicated that the atzA, -B, and -C genes are localized on a 96-kb self-transmissible plasmid, pADP-I, in Pseudomonas sp. strain ADP. High-performance liquid chromatography analyses showed that cyanuric acid degradation was not encoded by pADP-I. pADP-1 was transferred to Escherichia coli strains at a frequency of 4.7 x 10-2. This suggests a potential molecular mechanism for the dispersion of the atzABC genes to other soil bacteria.