Children born in Turku, Oulu and Tampere university cities in Finland are screened at birth for the HLA-DQB1 and DQA1 alleles that carry increased risk to or protection from development of type 1 diabetes. Children carrying increased risk are followed at 3-month intervals until 2 years of age and then at 6-12-month intervals until,15 years of age for development of diabetes-associated autoantibodies (autoantibodies against islet cells, insulin, glutamic acid decarboxylase and IA-2 protein). Children having at least two types of autoantibodies of the four measured in at least two consecutively drawn samples are randomized to receive daily intranasal insulin or placebo in a double-blinded 1:1 trial. Hypothesis is that intranasal insulin delays or prevents development of clinical type 1 diabetes. The primary outcome measure is development of clinical diabetes, but serum concentrations of autoantibodies, responses to intravenous glucose tolerance test and possible side effects of therapy are also closely monitored.