Glucose supply is less than required during early lactation. The glucose deficit affects the homeorhetic mechanisms that coordinate milk production and also impinges upon reproduction. The effect of glucose infusion during early lactation was tested. Postpartum dairy cows (n = 22) that calved in either the autumn (n = 11) or spring (n = 11) were treated with either glucose (GLUC; n = 11) or saline (SAL; n = 11). The GLUC cows received 750 g of glucose per day via continuous intravenous infusion of 40% dextrose solution (0.52 g glucose/min). The SAL cows received an equal volume of 0.9% saline. Infusions began during the second week postpartum (7.9 ± 1.9 d) and continued for 14 d. Blood was collected 4 times daily. Data were analyzed by using PROC MIXED of SAS. Compared with SAL, the GLUC cows had greater blood glucose concentrations (69.7 ± 1.5 vs. 61.7 ± 1.5 mg/dL; P < 0.01). There was a tendency (P < 0.11) for a treatment by season interaction for plasma glucose (spring: 71.6 ± 2.3 vs. 60.0 ± 2.5 ng/mL, P < 0.01; autumn: 67.7 ± 2.0 vs. 63.4 ± 1.8 mg/mL, P > 0.10; GLUC vs. SAL) and there was a treatment by season interaction (P < 0.01) for plasma insulin (spring: 4.4 ± 0.4 vs. 3.1 ± 0.4 ng/mL, P < 0.05; autumn: 3.4 ± 0.5 vs. 3.1 ± 0.5 ng/mL, P > 0.10; GLUC vs. SAL). GLUC cows had lesser plasma nonesterified fatty acids (NEFA; 448 ± 39 vs. 580 ± 39 µEq/L; P < 0.03) and lesser plasma β hydroxybutyrate (BHBA; 0.63 ± 0.10 vs. 1.15 ± 0.10 mM; P < 0.01). Insulin sensitivity (RQUICKI) was less in spring cows compared with autumn cows (0.50 ± 0.01 vs 0.53 ± 0.01; P < 0.05). There was no effect of treatment on milk produced (27.8 ± 1.1 vs. 27.8 ± 1.1 kg/d; GLUC vs. SAL) or as-fed consumption of total mixed ration (44.1 ± 1.6 vs. 45.1 ± 1.7 kg/d; GLUC vs. SAL). The number of cows with first ovulation during the infusion was not affected by treatment [5/11 (45%) for GLUC and SAL] and interval to first ovulation was similar (13.7 ± 0.9 d postpartum). There was a tendency (P < 0.10) for more autumn cows [7/11 (64%)] compared with spring cows [3/11(27%)] to ovulate during infusion. Glucose infusion affected plasma hormone and metabolite concentrations but did not affect milk production or interval to first ovulation.