For 18 patients after total pancreatectomy, serial determinations of plasma immunoreactive insulin bound with insulin antibody (binding IRI) were performed to ascertain the relationship between insulin antibody formation and diabetic stability. As a result, seven patients treated with human DNA insulin experienced neither unstable diabetic control (UDC) nor binding IRI elevation. On the other hand, six (58%) of 11 patients treated with beef and porcine insulins began to experience UDC with elevation of binding IRI. For these six patients, the binding IRI level was as low as 242 +/- 100 microU/ml at the onset of UDC and continued to increase (maximum binding IRI, 2048 +/- 1707 microU/ml) without spontaneous recovery from UDC. However, three patients recovered from UDC by the transfer to human DNA insulin, with a small decrease in binding IRI (470 to 4400 microU/ml) at the end of UDC. An equilibrium binding assay and the kinetic analysis of insulin antibodies showed that high-affinity antibody capacity (Ab1) for beef insulin was 28 +/- 6 ng/ml immediately before UDC, 306 +/- 120 ng/ml (115 to 578 ng/ml) during UDC, and 28 +/- 12 ng/ml immediately after UDC. Low-affinity antibody capacity was not correlated with diabetic stability. Therefore, in the totally pancreatectomized patients, it was concluded (1) that Ab1 was associated with the UDC onset or the recovery and (2) that UDC developed with far lower levels of Ab1, in contrast with patients with insulin-dependent diabetes. This is a reason why serial determination of insulin antibody, especially Ab1, is necessary for control of diabetes after total pancreatectomy.