To the Editor—The polyomavirus BK may cause progressive renal allograft failure in 1%–5% of kidney transplant recipients [1, 2]. The risk factors for BK virus nephropathy (BKVN) are not well understood but may involve rejection episodes and treatment with antilymphocyte preparations and potent new immunosuppressive drugs such as tacrolimus and mycophenolate mofetil [3]. Diagnosis of BKVN requires the immunohistochemical demonstration of BK virus–infected tubular epithelial cells in the allograft biopsy specimen. We note that detection of BK virus DNA in plasma closely follows the course of BKVN and may serve as a noninvasive tool for diagnosis and monitoring [4]. Recently, Limaye et al. [5] confirmed our findings in a retrospective study of 4 patients with BKVN and showed that the BK virus load decreased when the immunosuppressive treatment was reduced or when the renal allograft was removed