Brazilian pine (Araucaria angustifolia [Bert.] O.Ktze.) is an indigenous conifer of the southern region of South America, typically regarded as a sun-loving species. However, there is insufficient information on the species’ behaviour under different irradiances to characterise its plasticity to light. The purpose of this work was to measure some ecophysiological responses of Brazilian pine seedlings to three irradiance levels: 100, 45 and 10% full sunlight. Thirty seedlings were grown under each of the irradiance treatments and, after 5 months, growth parameters, leaf chlorophyll concentration and in vivo nitrate reductase activity, in both leaves and roots, were analysed. There was no increase in shoot biomass allocation in response to shading, in contrast to results from other experiments. Only low-light seedlings showed significant increase in specific leaf area, as well as in the ratio of height to shoot biomass. Chlorophyll content and the ratio of chlorophyll a to chlorophyll b did not vary among treatments. Nitrate reductase activity was detected only in roots and was reduced in the low-light treatment. An overall analysis of the results points to a normal growth of Brazilian pine seedlings at both high- and medium-light sites, at least in their initial stages of development.