Monocyte cytotoxic crossmatches were performed on the sera of all 164 patients on the Victorian transplant waiting list in order to determine the incidence of antimonocyte antibodies and to assess if prospective screening for these antibodies would be justified. Initially all current sera were screened without absorption by the cytotoxicity assay for the presence of antilymphocyte and antimonocyte reactivity against a panel of ten donors. Subsequently, a further 45 "peak"-reactive sera were screened against the same panel. Forty sera with monocyte specific reactivity were selected. MHC class I and class II antibodies were absorbed with pooled platelets and B lymphoblastoid lines, respectively. The absorbed sera were then screened against T cells, B cells, and monocytes of 38 donors for monocyte-specific antibodies. Seven sera from six recipients showed monocyte reactivity without T cell or B cell reactivity, with panel reactivity ranging from 3-29%. This gives an overall patient incidence of 3.6%, and when expressed as a percentage of consecutive crossmatches has a calculated incidence of 0.45%. This incidence is much lower than previously reported and would indicate that prospective crossmatching for antimonocyte antibodies would not be of benefit in this group of patients.