To evaluate the possibility of autoimmune processes against pancreatic islets in fetal life, we tested islet cell antibody (ICA) reactivity with 14 fetal pancreata obtained after abortion at the 15th up to the 19th week of gestation. Pancreatic islets positive for a monoclonal proinsulin antibody but non-reactive with ICA negative control serum were found in 9/14 pancreata and all (9/9) of them showed a positive reaction with the ICA standard. It is concluded that ICA reactivity may be detected in fetal human pancreata. Further studies on fetal islet cell antibody reactivity in the development of insulin dependent diabetes mellitus (IDDM) are warranted.