[Agglutinins in marine brown algae. Dedicated to Professor Dr. H. Knöll on his 65th birthday]

Extracts from the brown algae Fucus vesiculosus, F. serratus, and Halidrys siliquosa agglutinated human erythrocytes of groups A, B, O, and AB as well as erythrocytes from some animal species, ascites tumour cells from mice, and streptococci of many groups of the LANCEFIELD system. The extract of Chorda filum did not show haemagglutination but agglutinated ascites tumour cells and streptococci of a few groups.