Little is known about the effect of flowering on leaf photosynthesis. To understand why net photosynthesis (Anet) is lower in Mangifera indica L. leaves close to inflorescences than in leaves on vegetative shoots, we measured nitrogen and carbohydrate concentrations, chlorophyll a fluorescence and gas exchange in recently matured leaves on vegetative terminals and on floral terminals of 4-year-old trees. We used models to estimate photosynthetic electron fluxes and mesophyll conductance (gm). Lower Anet in leaves close to developing inflorescences was attributable to substantial de-creases in stomatal conductance and and also in photo-synthetic capacity as indicated by the decrease in the light-saturated rate of photosynthetic electron transport (Jmax). The decrease in was the result of decreases in the amount of foliar nitrogen per unit leaf area, and may have been triggered by a decrease in sink activity as indicated by the increase in the hexose:sucrose ratio. Parameters measured on leaves close to panicles hearing set fruits were generally intermediate between those measured on leaves on vegetative shoots and on leaves close to inflorescences, suggesting that the changes in Anet associated with flowering are reversible.