This invention is directed to the measurement of distances between adherent particles and the surface to which the particles are adhered. The particles may be artificial such as beads or natural such as cells and are labeled with a detectable label. The surface may be a biological surface such as a cell, a membrane or a biological structure, or an artificial surface such as plastic or glass. The factor by which a signal emitted from particles adherent to the surface differs from the detected signal is directly related to a factor specific for each medium which can be calculated. Knowing this factor and the value of the amount of label detectable from the particles, the distance between the particle and the surface can be determined. Such methods can be used to monitor the degree of spreading of cells along a surface such as an extracellular matrix, to determine the physical nature of the cell surface, or to determine the nature of cell-to-cell and cell-to-ligand receptor bridges. These methods can also be used in testing surfaces such as tissue culture products for relative adhesiveness and in testing other products for overall stickiness or smoothness. These methods can also be used to screen chemicals, drugs, protein and many other substances to determine if they have an effect on cellular adhesion and spreading.