We studied the guidance and activation of macrophages from the P388D1 cell line and rat peritoneum by topographic features on a nanometric scale. Cells were plated on plain fused silica substrata or substrata with microfabricated grooves and steps, 30-282 nm deep. The contact of cells with the patterned surface activated cell spreading and adhesion and increased the number of protrusions of the cell membrane. These changes were accompanied by an increase in the amount of F-actin in cells. The accumulation of F-actin and vinculin in cells was observed along the edges of single steps or grooves. Formation of focal contacts along discontinuities in the substratum was accompanied by the phosphorylation of tyrosine colocalized with F-actin and vinculin. A similar pattern of staining was seen in cells stained for vitronectin receptor, alphaV integrin, but not for integrins alpha5beta1 or alpha3beta1. Cells cultured on nanogrooves showed a higher phagocytotic activity than cells cultured on plain substrata. We show that macrophages can react to ultrafine features of topography of a size comparable to that of a single collagen fiber and become activated by the contact with topographic features.