Alkaline phosphatase (ALP) isoenzymes were measured in type 1 diabetics, type 2 diabetics and in a non-diabetic control group. Within the diabetics and the control group, intestinal ALP activity was significantly higher in BO secretors than A secretors or ABO non-secretors. There was no difference in intestinal ALP activity between type 1 and type 2 diabetics but the diabetics had a significantly higher activity of this isoenzyme than the corresponding blood group/secretor status category of the control group. Liver ALP was significantly higher in the diabetics compared with the control group. Bone ALP showed no significant difference between the diabetics and the control group.