Two Israeli expeditions to the Eritrean (then Ethiopian) coast in 1962 and 1965 obtained 127 specific and infraspecific taxa of benthic marine algae representing 73 genera and 4 species of seagrasses representing 3 genera. Collections were made mainly in the Dahlak Archipelago, but also on the adjacent mainland coast. The spring (1962) expedition yielded 94 species of algae, whereas the autumn (1965) expedition yielded 77, with 44 present in both seasons. Among these algae, 13 genera and 47 species had not been recorded previously from the Red Sea. Some of these 47 species have been reported subsequently from the northernmost part of the basin. There were 58 Rhodophyta, 33 Chlorophyta, and 31 Phaeophyta. Blue-green prokaryotes (Cyanophyta) were well represented in the collections, but only 5 species were identified. Two new species of algae are described: Pterocladia microscopica Lipkin et Papenfuss and Hypnea anastomosans Papenfuss, Lipkin et Silva. Two other new species have been published elsewhere: Turbinaria papenfussii W.R. Taylor and Chlorodesmis papenfussii Ducker. A new name, Sargassum steinitzii, is proposed for S. tenue J. Agardh, non S. tenue (Kützing) Endlicher. Two new combinations are made: Gelidiopsis capitata for Acrocarpus capitatus Kützing and Chondrophycus glanduliferus for Chondria glandulifera Kützing.