Objective To investigate the effect of ketamine on the phosphodiesterase (PDE) activities in lung tissue and leukocytes in rats. Methods Twenty SD rats weighing 140-160 g were randomly divided into two groups of 10 animals each : (A) ketamine group received intraperitoneal ketamine 10 mgkg-1 and (B) control group received equal volume of normal saline ip. Thirty minutes after ketamine administration the animals were sacrificed by exsanguination. Leukocytes were separated and 25 mg of lung tissue was obtained for determination of PDE activities by HPLC. Results The PDE activities in both lung tissue and leukocytes were lower in ketamine group than those in control group ( P