Fetal human pancreatic islets were cultured and cryopreserved for long periods (18 weeks and 6-8 months, respectively). Multiplication of the cells was observed, and later differentiation as well. The growth characteristics and insulin-like immunoreactivity were evidenced by light microscopy, immunocytochemistry, electron microscopic examinations and measurement of the total insulin content. These results indicate that the cultivation and storage of fetal islets by cryopreservation are hopeful procedures for future human islet transplantation.