The nature and origin of plasma immunoreactive glucagon (IRG) after pancreatectomy in humans remains controversial. Low plasma IRG levels and heterogeneity hamper accurate assessment. We studied plasma IRG levels and profiles in 12 patients 2-57 mo after a total pancreatectomy (with antrectomy and duodenectomy) for cancer (N = 9) or chronic pancreatitis (N = 3). After oral glucose, plasma IRG (with the COOH-terminal-specific 30K glucagon antibody) rose from 59 +/- 7 to a peak of 113 +/- 17 pg/ml at 60-120 min. Chromatographic profiles revealed four distinct IRG fractions. In every patient a plasma IRG fraction of 9000-15,000 Mr, detectable basally, increased markedly after oral glucose and accounted for the rise in total IRG observed in plasma. Nine of the 12 pancreatectomized subjects had no detectable 3500-Mr glucagon and the remaining 3 had very low levels. For the group as a whole, 3500-Mr IRG comprised 1-2% of the total recovered IRG. Two patients were also studied before pancreatectomy: suppressibility of glucagon (Mr 3500) was evident. After surgery this paradoxical response to oral glucose was demonstrated. Reproducibility of these responses was confirmed in two patients studied twice over 2 yr. Diabetic controls without pancreatectomy did not show this response. The absence or marked reduction of pancreatic glucagon was confirmed in five of the pancreatectomized patients after intravenous arginine or oral protein. Normal basal plasma IRG and profiles, oral glucose suppressibility, and arginine stimulation were present in five control patients with unresectable pancreatic malignancies.(ABSTRACT TRUNCATED AT 250 WORDS)