Living cells embedded in a complex Extra–Cellular Matrix (ECM) migrate in a sophisticated way thanks to adhesions to matrix fibres and contractility. It is important to know what kind of forces are exerted by the cells. Here we use reflectance confocal microscopy to locate fibres accurately and determine displacement fields. Correlation techniques are used to this aim, coupled with proper digital image processing. Benchmark tests validate the method in the case of shear and stretching motions. Finally, the method is tested successfully for studying cancer cells migrating in collagen gels of different concentration. KEYWORDS: Displacement field, phase correlation, confocal microscopy, cell migration, fibres, cancer cells.