This paper describes the influence of the composition of poly(dimethylsiloxane) (PDMS) on the attachment and growth of several different types of mammalian cells: primary human umbilical artery endothelial cells (HUAECs), transformed 3T3 fibroblasts (3T3s), transformed osteoblast-like MC3T3-E1 cells, and HeLa (transformed epithelial) cells. Cells grew on PDMS having different ratios of base to curing agent: 10:1 (normal PDMS, PDMSN), 10:3 (PDMSCA), and 10:0.5 (PDMSB). They were also grown on "extracted PDMS" (normal PDMS that has reduced quantities of low molecular-weight oligomers, PDMSN,EX) and normal PDMS that had been extracted and then oxidized (PDMSN,EX,OX); all surfaces were exposed to a solution of fibronectin prior to cell attachment. Generally, fibronectin-coated PDMS is a suitable substrate for culturing mammalian cells. Compatibility of cells on some surfaces, however, was dependent on the cell type: PDMSN,EX,OX caused cell detachment of 3T3 fibroblasts and MC3T3-E1 cells, and PDMSCA caused detachment of HUAECs and HeLa cells. Growth of cells on PDMSN, PDMSN,EX, and PDMSB was comparable to growth on tissue culture-treated polystyrene for most of the cell types. All cells grew at similar rates on PDMS substrates regardless of the stiffness of the substrate, for substrates having Young's moduli ranging from E = 0.60 +/- 0.04 to 2.6 +/- 0.2 MPa (for PDMSB and PDMSN,EX, respectively).