OBJECTIVE To explore the clinical value of determination of ATP levels in CD4(+) cells of patients with cytomegaloviral pneumonia after kidney transplantation. METHODS Twenty-eight patients with cytomegaloviral pneumonia following kidney transplantation and 30 healthy volunteers were enrolled in this study. ATP-bioluminescence assay (ATP-CVA) was used to assess the immune response of CD4(+) cells to phytohemagglutinin (PHA) stimulation in the normal volunteers and the recipients (before and at 1, 2, and 4 weeks after renal transplantation, before and at 2 and 4 week after the treatment). RESULTS ATP concentration in CD4(+) cells of the recipients was 402-/+58 ng/ml before the operation, significantly lower than that in normal volunteers (458-/+196 ng/ml, P<0.05), and reached the lowest level in the first week after operation especially in the recipients with antibody-inducing therapy; ATP level increased slowly since week 2 post-operation, but still remained significantly lower than the preoperative by the fourth week (266-/+87 ng/ml, P<0.05), especially in the recipients receiving antibody-inducing therapy. In the event of cytomegaloviral pneumonia, ATP level underwent a mild reduction to 152-/+78 ng/ml in comparison with the postoperative level at the first week (P>0.05), and was significantly lower than preoperative level (P<0.01); the decrease was especially obvious during the exacerbation of the condition. ATP level then increased slowly after effective treatment, but was still lower than the preoperative level at 4 weeks after the operation (336-/+92 ng/ml, P<0.05). CONCLUSIONS The determination of ATP level in CD4(+) cells allows more accurate assessment of the cellular immunity in the renal transplant recipients with cytomegaloviral pneumonia to help in the clinical treatment of the patients.