Diabetes mellitus in childhood is connected to several immunological phenomena which per se do not prove that immunological mechanisms do cause the beta cell destruction, as such mechanisms could be just secondary. However, there is now evidence which strongly supports the autoimmune hypothesis, like the beta-cell destruction in the transplant given from a healthy twin to the diabetic monozygotic co-twin, the effect in newly-diagnosed diabetes of immunosuppression, the passive transfer in experimental animals of an immune process creating diabetes etc. Several facts such as presence of activated T-cells in the insulitis indicate that the cell-mediated immunity is important, while it is still debatable whether humoral factors, and if so which, alone could be responsible for the beta cell destruction. Recently interleukins and other lymphokines have shown to be of great interest as well as the release of free radicals. This knowledge opens new views on the possibility to put an end to or even prevent the beta cell destruction. Rough immunosuppression with cytostatics or cyclosporin has such severe side-effects that such therapy is contra-indicated at least in children. Until more specific therapies are discovered e.g. vaccination with lymphoblasts or blocking the autoantigens with monoclonal antibodies, supportive measures to protect the beta cells may be one practical way.