The interaction between polymer particles with an immune ligand on their surfaces and normal (hepatocytes) and malignant (Raji) cells with a corresponding membrane receptor was investigated by scanning and transmission electron microscopy. The influence of time, temperature, and anti-metabolites on this process was studied. The results indicate that when particles with an immunoligand are added to cells with a corresponding membrane receptor, three successive steps are initiated, the first two of which are not dependent on the temperature or the metabolic state of the cells. The first step in this process is the binding of particles to the cell surface through the immunoligand on the particle and the receptor on the cell surface. The initial binding formed by immunoligand and corresponding receptor is followed by a stronger interaction between cell and particle. This second step seems to be governed by a successive antibody-antigen interaction: the zipper mechanism. A third step in the particle-to-cell interaction is characterized by movements of the cellular surface, as revealed by membrane folds, pseudopods, and lamellae extending from the surface and enveloping large parts of the particle.