Electronics miniaturization techniques have been used to fabricate substrata to study contact guidance of cells. Topographical guidance of three cell types (BHK, MDCK and chick embryo cerebral neurones) was examined on grooved substrata of varying dimensions (4-24 microns repeat, 0.2-1.9 microns depth). Alignment to within 10 degrees of groove direction was used as our criterion for guidance. It was found that repeat spacing had a small effect (alignment is inversely proportional to spacing) but that groove depth proved to be much more important in determining cell alignment, which increased with depth. Measurements of cell alignment and examination by scanning electron microscopy showed that BHK cells and MDCK cells interacted differently with grooved substrata, and also that the response of MDCK cells depended on whether or not the cells were isolated or part of an epithelial cell island. Guidance by a multiple topographical cue is greater than could be predicted from cells' reactions to a single cue (Clark et al. Development 99: 439-448, 1987). Substratum topography is considered to be an important cue in many developmental processes. Cellular properties such as cytoskeletal organisation, cell adhesion and the interaction with other cells are discussed as being factors determining a cells susceptibility to topography.