To evaluate serum levels of CD30 for prediction and diagnosis of acute kidney allograft rejection. Prospectively, we measured serum levels of CD30 before kidney transplantation (initial CD30), 3-5 days postoperatively (postoperative CD30), and at creatinine rise episodes. The predictive value of CD30 for diagnosis of AR within the 6 postoperative months was assessed in 203 patients. Serum levels of the initial and postoperative CD30s were 58.10 ± 52.55 mg/dL and 51.55 ± 49.65 mg/dL, respectively (P=.12). Twenty-three patients experienced biopsy-proven acute rejection, 28 had acute allograft dysfunction due to non-immunologic diseases, and the remaining 152 had normal creatinine levels. The initial CD30 was not different between patients with and without AR (P=.77). Multivariate analysis demonstrated that postoperative CD30 was associated with AR (86.46 ± 80.01 mg/dL in AR positives versus 47.10 ± 42.65 mg/dL in AR negatives; P=.03). The sensitivity and specificity of postoperative CD30 >41 mg/dL were 70% and 60%, retrospectively (area under the curve =0.68; 95% confidence interval =0.57-0.80). Although CD30 at creatinine rise was higher in patients with AR than those with other causes of creatinine rise, the reverse correlation of the time of creatinine rise with AR and CD30 precluded the evaluation of the CD30 measured at this time. Posttransplantation CD30 levels are higher in patients with acute rejection, but its clinical value requires further investigation. To elucidate the diagnostic value of CD30, we should better understand factors that influence this marker postoperatively.