The photosynthetic rate of Antarctic mosses and lichens was studied with investigations into the effects of high levels of light radiation and of possible UV effects. The mosses Pottia heimii, Bryum argenteum, B. pseudotriquetrum, Ceratodon purpureus and Sarconeurium glaciale had their photosynthetic performance monitored for full diel results under natural light conditions. Continuous ... measurements of photosynthetic rates together with all environmental parameters and light harvesting systems were measured. Concurrently, fluorescence measurements were also made. Further detailed studies were carried out on B. argenteum where photosynthesis and fluorescence was measured from plants kept in two conditions (deep shade and normal light conditions). The experiment was repeated with the UV component of sunlight filtered out. The photosynthesis of Umbilicaria aprina (a large lichen common at Botany Bay) was studied with light-response curves and water content curves constructed, several diel measurements made and the minimum temperature for photosynthesis investigated. A full study was carried out on Buellia frigida where the CO2 exchange and fluorescence yield were compared. The microclimate was recorded in a rich lichen/bryophyte location in Botany Bay. Measurements were made continuously from 12 January to 2 February, 1992. In the 1999-2000 season the photosynthetic response to temperature and light of two moss species Bryum subrotundifolium and Ceratodon purpureus was measured.