Ribosomes and rRNAs were isolated from cells of green-blue alga Anabaena variabilis. The sedimentation properties of the ribosomes as well as density, molecular weights and nucleotide composition of rRNAs were determined. The ribosomes were found to have the S20,w value equal to 67.2+/-0.4S, whereas those of the ribosome subunits were 48.6+/-0.8 and 29.5+/-1.1S. The buoyant density of the ribosomes in CsCl was 1.641+/-+/-0.002 g/cm3; a calculated relative protein content was 35%. The molecular weights of rRNAs estimated by electrophoresis in PAAG containing 0.5% agarose, are 1.1-10(-6) and 0.56-10(6) daltons. The nucleotide composition of rRNA was determined and rRNA was shown to belong to the GC type. Consequently, the blue-green alga ribosomes do not differ in the parameters studied from bacterial ribosomes.