Measurements of the photosynthesis-light response of flag leaves in a winter wheat crop were made during the period from maximum elongation until complete senescence. Immediately following leaf elongation, the maximum rates of photosynthesis and the values of efficiency at low light were in the range 2.8–3.6 g CO2 m−2 h−1 and 8–11 μg CO2 J−1 respectively. The shape of the photosynthesis-light response remained constant throughout and was close to a ‘Blackman’ type response rather than a rectangular hyperbola. The results were analysed, therefore, using a more recent model which is a non-rectangular hyperbola. Stomatal and internal resistances were equally important in limiting the maximum rate of photosynthesis.