CA 19-9 is a monoclonal antibody-defined tumor marker expressed by exocrine pancreas. It has been shown that exocrine atrophy was associated with deficiency. Hyperamylasemia has been described during ketoacidosis. Our study aimed at investigating the relationships between CA 19-9 and metabolic control of diabetes. Study was performed on 51 adult consecutive diabetic patients (21 type 1 and 30 type 2), with ketoacidosis or hyperosmolarity (group A, n = 15), poor glycaemic control (group B, n = 19), or good control (group C, n = 17). Serum CA 19-9 and metabolic parameters were evaluated on day 1 and day 30. Analysis of variance showed a very significant global difference between groups for CA 19-9 (p less than 0.0001); group A (66.1 +/- 11.4 u/ml) significantly differed from group B (36.4 +/- 4 u/ml) (p less than 0.01) and group C (22.4 +/- 2.8 u/ml) (p less than 0.001). Simple regression showed a significant correlation between CA 19-9 and fasting blood glucose (r = 0.6, p less than 0.001), plasma creatinine level (r = 0.37, p = 0.01), bicarbonate (r = 0.47, p = 0.001) and HbA 1c (r = 0.33, p = 0.032). The Ca 19-9 decrease on day 30 paralleled the improvement of glycaemic control. We conclude that CA 19-9 in diabetic patients is raised in acute metabolic situations and correlated very well with blood glucose concentration. A careful interpretation of this tumor marker assay is required when screening for pancreatic carcinoma among diabetic patients. CA 19-9 could be a useful and sensitive marker for the severity of exocrine damage and functional cellular disorders following metabolic disturbances in diabetes.