Pseudocholinesterase (PChE) activity in plasma, liver, pancreas and adipose tissue of alloxan-diabetic rats has been determined. 48 hours after the induction of diabetes an increase of PChE activity in plasma and a decrease in liver and adipose tissue was observed. After that, the activity in plasma remained at the same level, in the liver it slowly rose to the control values and in adipose tissue significantly increased beyond the control values. Significant changes of PChE activity in the pancreas were not noticed. Female rats had higher PChE activity in plasma and liver than the male, but in the pancreas and adipose tissue there were no sex differences. On the basis of our results it seems possible to propose that PChE is synthesized also in adipose tissue, but the synthesis is regulated by different mechanisms than those in the liver.