Portions of pancreases from 19.5-day fetal rats were grown in organ culture on two types of liquid media: low glucose, containing 162 to 170 mg. glucose/100 ml.; high glucose, containing 1,031 to 1,073 mg. glucose/100 ml. Following four days of organ culture, the tissues were extracted and assayed for insulin content (immunoassay). Other cultures were transplanted to maternal hosts at two sites: beneath the capsule of the kidney and into the anterior chamber of the eye. Ten days later, the transplants were removed and assayed for insulin content.

Large quantities of immunologically active insulin were present in the culture media following forty-eight and ninety-six hours of incubation. Expiants exhibited a four- to sixfold increase in insulin content following four days in vitro. Pancreatic expiants cultured on the high glucose medium contained less extractable insulin than similar ex-plants cultured on the low glucose medium.

When cultured expiants were transplanted to hosts with normal blood glucose levels, the total extractable insulin content of the grafts was 55 per cent to 130 per cent greater than that at the time of transplantation. When cultures were transplanted to alloxan diabetic hosts, the total extractable insulin content of the grafts was less than that found in grafts to normal hosts.

A small but statistically significant drop in blood glucose level was observed in hyperglycemie diabetic maternal hosts receiving transplants of organ cultured pancreas.

These results indicate the continued growth and functional responsiveness of the islet beta cells during organ culture and following subsequent transplantation.