Abstract This research documented the metabolic changes associated with the use of budbreak promoter sprays in vineyards. The objective was to evaluate metabolic heat production (Rq) and respiratory ( R C O 2 ) rates and water content of Vitis vinifera L. cv. ‘Flame Seedless’ buds during dormancy, and after spraying with the budbreak promoter, hydrogen cyanamide (H2CN2), assessing its effect on the developmental response of buds through several phenological phases in the vineyard. The study was conducted in the winter from November 24, 2005 to February 8, 2006 using isothermal calorimetry at 25 °C. Phenological stages monitored were dormant bud, swollen bud, half-inch green, first-flat leaf and second-flat leaf. On December 23, when 97 chilling units had accumulated, H2CN2 (0.82 M divided into two applications of 0.47 and 0.35 M) was applied and compared with untreated controls. Metabolic heat rates significantly (p ≤ 0.05) increased from endodormant buds to the half-inch green stage, from 2 to 33 μW mg−1 dry weight (dw). This occurred from November 24 to January 15. Bud respiration rate showed a similar pattern, increasing from 3.7 to 346 nmoles CO2 s−1 mg−1 dw, and bud water content increased from 2.2 to 5.6 mg mg−1 dw. In a 27-day period after spraying, treated vines reached 50% budbreak, while controls reached only 7%. Phenological development was heterogeneous due to insufficient chilling, as well as to low temperatures following H2CN2 application. Changes in Rq and R C O 2 were detected 12 days in advance compared with changes in bud hydration.