Transplantation of isolated islets of Langerhans in diabetic patients is frequently followed by an early loss of function due to acute rejection. Since the primary target of host-vs-graft reaction is the endothelium of the microvessels, it is of great importance to analyze the microcirculation of freely grafted pancreatic islets. For this purpose we present a new model, allowing for intravital microscopy of the microvasculature of transplanted islets of Langerhans. The islets are isolated from Syrian golden hamsters and DA-rats, respectively, by a modified collagenase digestion technique. Subsequently, the islets are transplanted into a hamster dorsal skinfold chamber. Using intravital fluorescence microscopy and video techniques, the microcirculation of the islet grafts can be observed repeatedly over a time period of up to four weeks. Quantitative analysis of the microhemodynamics, i.e. functional capillary density, capillary RBC-velocity and microvascular diameters, can be performed by means of a computer assisted image analysis system. In addition, the model allows for investigation of the flow behaviour of white blood cells and their interaction with the endothelium of the microvascular segments. For the first time a model is presented, enabling for in vivo analysis of the revascularization process and microcirculatory function of transplanted islets of Langerhans. Furthermore, the model allows to assess microvascular phenomena during host-vs-graft reaction as well as effects of immunosuppressive regimens.