The most effective form of treatment for chronic renal failure is kidney transplantation from a cadaver or a living donor. For a kidney transplant to be successful, tissue compatibility and a lack of donor-specific anti-human leukocyte antigen (H LA) antibodies in the circulation of the patient are vital, in addition to ABO blood group compatibility. The presence of anti-HLA antibodies. is assayed before transplantation using various methods, but because organ rejections have been observed in previous studies, different techniques are required to detect anti-FILA antibodies. Today, flow cytometry crossmatching is one of the most important and effective techniques in testing for donor-specific anti-HLA antibodies (DSAs). If weakly positive serum is assayed after serial dilution, it can yield high positivity. Herein, we describe the differences between the results for diluted and undiluted weakly positive sera studied using the flow cytometry crossmatch (FCXM) technique. In a recent study, the sera of weakly FCXM-positive patients were diluted 1/50, and the FCXM test was repeated. The use of diluted serum eliminated the effect of the prozone so that the DSAs could be detected.