The relationship between serum concentrations of glucose, insulin and glucagon during the first two days of life was studied in healthy newborns. The first capillary blood sample was obtained at 3-15 h of age (median 6 h; day 0) and a second sample approximately 24 h later (day 1). Serum glucose concentrations in the first sample averaged 2.1 +/- 0.07 mmol/l (mean +/- SEM; n = 60) and were positively correlated with postnatal age (p < 0.01). Serum glucagon concentrations in the first sample averaged 570 +/- 32 pg/ml and were inversely correlated with glucose concentrations (p < 0.0001). At the second sampling, serum glucose concentrations had increased to 2.9 +/- 0.07 mmol/l (p < 0.001; n = 57) and serum glucagon concentrations had decreased to 403 +/- 22 pg/ml (p < 0.001). Serum insulin concentrations were 11.7 +/- 0.3 microU/ml and 10.2 +/- 0.3 microU/ml at the two samplings and did not correlate with serum glucose concentrations. The relationship of serum glucose and hormone concentrations to maternal and infant characteristics was studied by stepwise regression analysis. Serum glucose concentration on day 0 was positively correlated with postnatal age (p < 0.01) and birth weight (p < 0.05) but inversely correlated with duration of labour (p < 0.05). Serum glucose concentration on day 1 was positively correlated with birth weight (p < 0.0001) and inversely correlated with maternal prep-pregnancy weight (p < 0.05). Similar analyses of serum hormone concentrations did not demonstrate any relationships with maternal or infant characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)