The distribution of different celltypes (A, B, D and PP cells) of the endocrine pancreas was studied in both the normal and in the experimental diabetic non-pregnant and pregnant rat. In the normal rat the head (juxta duodenal part) of the pancreas contained more PP cells than the tail (12.5±1.1 versus 5.2±2.2) but fewer glucagon cells (19.0 ±3.5 versus 14.3±3.6). This difference disappeared during pregnancy, when the total B cell mass increased (2.05 versus 0.82). In the diabetic rat no difference was found in the number of endocrine cells between the tail and the juxta duodenal part of the pancreas. Unlike the non-diabetic rat, the number of B cells did not increase in the pancreas of the pregnant diabetic rat. An absolute increase in the number of glucagon (A) cells was demonstrated in the islets of the pregnant diabetic rat as compared to the non-diabetic rat (35 versus 21.2).