Preparations of RNP-particles from rat sarcoma M-1 were obtained by means of treatment with different detergents: anione - sodium deoxycholate (1%) and non-ionic - Triton X-100 (1%). Triton X-100 caused some increase in content of the small ribosomal subunit and also in the content of 21 S and 7.5 S particles in the preparation. The latter particles as well as ribosomes were resistant to different detergents. 21 S RNP-particles were stable in 1 M KCl. In a cell-free system 21 S and 7.5 S RNP-particles lost a significant amount of labelled protein, which appeared partially in the ribosomes.