Aims/hypothesis. This study was undertaken to investigate metabolic and genetic characteristics of latent autoimmune diabetes in adults (LADA).¶Methods. We evaluated insulin secretory capacity with oral and intravenous glucose tolerance tests (early insulin response) and hyperglycaemic clamp (insulin secretory capacity) and the rates of whole body glucose uptake with the euglycaemic clamp, HLA-DQB1 genotypes (time-resolved fluorescence) and islet cell antibodies (ICA) (immunofluoresence) and antibodies to glutamic acid decarboxylase (GAD) (radio-immunoprecipitation) in 36 non-diabetic offspring (LADA-offspring) of patients with Type II (non-insulin-dependent) diabetes mellitus who tested positive for ICA and/or GAD antibodies during the 10-year follow-up from the diagnosis and in 19 healthy control subjects without a family history of diabetes.¶Results. The early insulin response during the first 10 min of an intravenous glucose tolerance test was about 40 % lower in the LADA-offspring than in the control group (p = 0.008). Insulin secretory capacity in the hyperglycaemic clamp was also about 30 % lower in the LADA-offspring (p = 0.048). The rates of whole body glucose uptake were similar in both groups. The frequency of low risk HLA-DQB1 genotypes was higher in the LADA-offspring than among Finnish healthy blood donors (p = 0.033). The risk conferring genotypes were associated with the lowest tertile of insulin secretory capacity in the LADA-offspring (p = 0.032). There were no associations between the autoantibodies and early insulin response or insulin secretory capacity within the study groups.¶Conclusion/interpretation. We conclude that LADA is a familial disease involving most likely gene defects leading to a slow progressive beta-cell destruction and insulin deficiency. [Diabetologia (2000) 43: 69–78]