Implant materials have been shown to induce inflammatory responses by human peripheral blood mononuclear cells (PBMC) in vivo. The inflammatory response to metals in vivo is characterised by the production of cytokines with inflammatory and osteolytic effects. Metals used for weight bearing implanted medical devices such as hip replacements were tested in this study for their ability to invoke an inflammatory response by PBMC in vitro. The metals used were commercially pure titanium (Ti), nickel chrome (NiCr) and cobalt chromium (CoCr). The inflammatory response by peripheral blood mononuclear cells to metal discs was assessed using an in vitro cell culture system. The cell culture model yielded two heterogeneous populations an adherent one comprised predominantly of macrophages (63 + 7 %, average + SEM) accompanied by a lower but statistically Significant percentage of T lymphocytes (34 + 6%) and a non-adherent population that was predominantly composed of T lymphocytes (7643 %), but also included a proportion of macrophages (14+2 %). Glass discs (control material) showed that equal percentages of T lymphocytes (484+5%) and macrophages (49+5%) had adhered. The overall number of cells adherent to glass (22000 + 4000) was lower than on Ti (105685+ 10000), NiCr (164116 + 5000), CoCr (82799 + 5000) demonstrating the role of surface properties in directing cellular adhesion. Cell adhesion was visualised by laser confocal fluorescent microscopy using single-cell-type T lymphocytes and/or macrophage cultures (95+ % pure) that were fluorescently stained prior to culture. The results confirmed that T lymphocytes were capable of adhering to metal surfaces when co-cultured with macrophages and also when in purified single cell type cultures. All the metals used induced an increase in the release of the proinflammatory cytokines TNFa, IL-6, IL-8 and IL-10, (in comparison to glass control) from PBMC with no change in IL1B secretion. There were no correlations between the concentrations of ions detected in the media and cytokine levels measured. All the cell culture conditions used resulted in cells with the potential for secreting the aforementioned cytokines. This was determined by qualitative analysis of mRNA transcription by reverse transcription PCR, and analysis of secreted cytokines. Ti induced an increase in the concentration of released TNF-c from 10 pg/ml (glass) to 89 pg/ml, IL10 increased from 78 pg/ml (glass) to 175 pg/ml, IL-6 increased from 5133 pg/ml (glass) to 25837 pg/ml, and the levels of IL-8 rose from 1309 pg/ml to 113481 pg/ml. The response to NiCr and CoCr was also higher than that to glass. In conclusion: No direct link was found between inflammatory cytokine production and free metal ion measured in the media, this does not rule out the contribution of metal ions to the inflammatory response seen. Only small differences in the scale of cytokines secreted in response to the different metals were detected, indicating that similar mechanisms of activation may have been invoked. Adhesion appears to be the mechanism behind initial PBMC activation and cytokine secretion, the higher levels of cytokines from PBMC cultured with metals could be due to the higher numbers of PBMC adhering to these surfaces compared to glass.