Microfilament-membrane attachment sites are complex structures that are essential for tissue differentiation in animals. In this article, we focus on the assembly and dynamics of such contact sites as seen in two cell types differentiating in cultures of the embryonic chicken heart, cardiocytes and fibroblasts. Concentrating on the cytoplasmic domain, we refer to previous biochemical, light, and electron microscopic studies on the structure and dynamics of these regions and supplement them with our own recent data. Although many details are still to be elucidated, we would like to propose the following model. Actin, alpha-actinin and vinculin are the major structural components of all microfilament-membrane contacts. Various subtypes of junctions are characterised by additional structural components or by specific isoforms. Temporal regulation of contact sites is linked to assembly and disassembly of microfilaments and might be controlled by special regulatory proteins. Finally, the cytoplasmic domains of junctional complexes may serve as structural matrices for the positioning of proteins involved in signal transduction pathways.