Transplantation of islets of Langerhans is a possible future therapy for insulin-dependent diabetes mellitus. In contrast to total pancreas, isolated islets of Langerhans can be treated prior to transplantation to reduce their immunogenicity. Thus the success rate in allotransplantation of islets can be increased. The isolation of large amounts of islets from human pancreas is still a problem and islets from different donors have to be collected and stored by cryopreservation. In this paper we describe the methods used in our laboratory to isolate islets of Langerhans from rodent, monkey and human pancreas. The results are presented of successful cryopreservation of these islets. Firstly, by a more conventional freezing method using dimethylsulfoxide as cryoprotectant. Secondly, by vitrification using a mixture of cryoprotectants. The latter method has not been used previously for cryopreservation of islets. The integrity of the islets before and after freezing was tested in vitro and, for mice, in vivo.