The flow cytometric lymphocyte crossmatch is a standard technique for evaluating the compatibility of potential kidney transplant recipients and donors. Recipient serum is incubated with donor lymphocytes and the latter are analysed in a flow cytometer for the presence of bound IgG antibodies. An increase in the level of IgG binding compared to a negative control indicates the presence of donor-specific antibodies which may lead to deleterious graft function. Described here is a method to perform T and B lymphocyte crossmatching in the same tube to detect IgG donor-reactive antibodies.