Observations have been made on the gas exchange and morphology of Vaccinium myrtillus taken from altitudes of 200 m, 610 m and 1,100 m along an altitudinal gradient in central Scotland. Under saturating irradiance, optimum temperatures and a range of vapour pressure deficits, photosynthetic rate and stomatal conductance increased with the altitude of origin of the populations. Correlated with these increases was an increase in the adaxial stomatal density with altitude. This response to altitude could be simulated in controlled conditions, by growing plants in a CO2 concentration below ambient, similar to that expected at altitude.Plant height decreased with altitude, a feature which was maintained in cultivation. Stem rigidity declined with altitude, in a manner which is predicted to limit the reproductive capacity of the population from 1,100 m in high wind speeds.Total leaf nitrogen increased with altitude. The nitrogen economy of the shoot is discussed in terms of nitrogen availability for stems and leaves and its control over maximum rates of photosynthesis, competitive ability and reproductive capacity.