The biological effects of mineral particles in both macrophage-like and fibroblast cell lines are described. The several macrophage-like cell lines available are all sensitive to the toxic effects of silica, but not all are equally affected by mineral fibres. The effects of the fibres are partially determined by their ability to interact with the cell surface and this has been monitored by density gradient centrifugation of cell-fibre mixtures. It has been found that the adhesion between fibres and cells is similar to that between cells and normal tissue culture surfaces. This adhesion requires fibronectin and involves arginine-glycine-aspartate (RGD) receptors on the cell surface. Using polylysine to render the fibres positively charged, short-term responses to fibres may be studied and this has revealed a size-dependent activation of the second messenger pathways. Such a response is difficult to monitor in normal cultures, as the response is asynchronous, but the use of microfluorimetric methods has enabled studies on single cells.