Aims: To investigate the biodegradation of the explosive compound RDX in Rhodococcus strain DN22, a bacterium previously isolated for its ability to grow on RDX as sole nitrogen source. Methods and Results: Analysis of the rates of RDX degradation and nitrite production indicated that 2 mol nitrite were produced per mole RDX degraded. Cells of strain DN22 had the highest activity against RDX during the exponential phase and low activity in the stationary phase. Nitrite production from RDX was inhibited by metyrapone, menadione, piperonyl butoxide, n -octylamine and carbon monoxide and inducible by pyrrolidine, pyridine and atrazine. Acridine orange treatment yielded RDX-minus derivatives of strain DN22 at a curing rate of 1.5% and all of the cured derivatives had lost a large plasmid. Conclusions: RDX biodegradation in strain DN22 appears to involve a plasmid-encoded cytochrome p-450 enzyme. Significance and Impact of the Study: Plasmid-borne RDX degradation genes could potentially be transferred between bacteria. Our research into RDX metabolism in strain DN22 will facilitate future applications of this bacterium for bioremediation.