The results of a study on the benthic macroalgal flora and vegetation of Terra Nova Bay (Ross Sea) carried out during the Italian expeditions to Antarctica made in the years 1987/88, 1989/90 and 1993/94, are presented. The flora is rather poor (9 Rhodophyceae, 4 Fucophyceae, 4 Chlorophyceae), but richer than that known from adjacent areas. The vegetation is on the whole characterized by a prevalence of sciaphilous species among whichIridaea cordata, Phyllophora antarcticaandClathromorphum lemoineanumdominating in the upper infralittoral, lower infralittoral and circalittoral zones, respectively. Moreover, the results of a study on biomass of a population ofI. cordataas well as of a population ofP. antarctica,carried out in the austral summer 1993/94, are reported too. The values of the biomass of the population ofI. cordataresulted to vary inversely with respect to those of the population ofP. antarctica.