The influence of methylmethacrylate monomer (MMA) on the cellular integrity of monocytes, granulocytes and endothelial cells in vitro was investigated. Clinically relevant blood concentrations of MMA (i.e., 5-10 micrograms/mL) were clearly cytotoxic to all cell types studied, as evidenced by the release of lactic dehydrogenase (LD) and 51Cr, and increased uptake of trypan blue (vital staining). Scanning electron microscopic examination of cells treated with 10 micrograms/mL MMA showed marked signs of cytotoxicity after 1 min incubation, and after 30 min the majority of the cells were totally disintegrated. These findings may have clinical bearing on intraoperative cardiorespiratory dysfunction and deep vein thrombosis in MMA-fixed joint replacement surgery.