The following comments are in response to concerns of Juan C. Scornik, MD, regarding our article entitled “Identification of high- and low-risk second kidney grafts” (1). Standardization of the flow cytometry crossmatch (FCXM) is indeed important (2). Ideally, in a prospective multicenter trial, each center would run calibration beads with each test to ensure that the fluorescence scales were similar. Furthermore, each center would use the same reagents and control sera. The retrospective FCXM data that were analyzed in our multicenter study were generated at each center in three independent studies of second kidney allograft survival during the years 1984 to 1991. Each center's FCXM data were logarithmically acquired data expressed as channel values and not as linear values. Channel values are proportional to fluorescence intensity. The proportionality is not linear, however; it is logarithmic. Each center independently established the FXCM test to be positive by use of “channel shifts.” Channel shifts were expressed as relative to individual negative control sera channel values, e.g., ≥9 on a 256-channel scale and ≥40 on a 1024-channel scale. Two centers expressed channel values at a 256-channel resolution and the third center expressed channel values at a 1024-channel resolution. FCXM channel shift data expressed on the 256-channel scale were multiplied by four. Thus, effectively, all FCXM data in Table 1 (1) were expressed as channel shift values at a 1024-channel resolution. Alternatively, it would have been correct to divide the channel shifts of the 1024 scale by four and express all FCXM data at a 256-channel resolution. A channel shift of 77 on a 1024-channel, 4-decade log scale does represent a doubling of fluorescence intensity and not antibody as stated(1). FCXM-positive T-cell channel shifts were greater in the low-risk subset with previous graft survival time (PGST) >3 months as compared with the high-risk group with PGST ≤3 months (P=0.001, two-groupt test; 1). This suggests that the levels of FCXM fluorescence intensities representing IgG antibodies are apparently less important than the combination of the duration of PGST and a positive FCXM test. However, all kidney graft recipients have some risk of early graft failure, even FCXM-negative second graft recipients. A positive FCXM and second kidney graft risk are well documented. FCXM-positive second kidney grafts have worse graft survival than FCXM-negative grafts, as shown in Figure 1 and in other referenced reports in the article (1). The key point in our article is that there are subsets of high-risk and low-risk FCXM-positive graft recipients as stratified by duration of PGST shown in Figure 2 (1). However, there are no FCXM risk-free second graft recipients, as demonstrated by a 15% rate of early regraft loss at 6 months in FCXM-negative patients with short and long PGSTs. FCXM and first kidney graft risk was not the subject of our article. However, many reports demonstrate a correlation with early primary graft failure or poor long-term outcome and a positive FCXM(3-8), but not all reports(9-13). Low- and high-risk FCXM-positive primary graft subsets are not readily identifiable before transplantation. Perhaps, therefore, all FCXM-positive primary cadaveric donor transplants should be deferred until the FCXM test is negative, because every cadaveric kidney graft counts. Richard J. Mahoney1,2 Douglas J. Norman3 Beth W. Colombe4 Marvin R. Garovoy4 Donald A. Leeber5 Kenneth A. Ault6 Immunogenetics Laboratory and Hematology Research Laboratory; Maine Medical Center Research Institute; South Portland, Maine 04106; Medical Transplantation Program; Oregon Health Sciences University; Portland, Oregon 97201 Immunogenetics and Transplantation Laboratory; University of California-San Francisco, UCSF School of Medicine; San Francisco, California 94143; Nephrology Division/Renal Transplantation Service Maine Medical Center; Portland, Maine 04102