Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was used to explore noncovalent interactions between different peptides and ribose nucleic acids (RNAs). One RNA was mixed together with two or more peptides or vice versa to compare the different effects of the molecules for noncovalent complex formation. The matrix 2,4,6-trihydroxyacetophenone was considered optimal for these studies due to the fact that peptides and RNA showed roughly the same peak intensities, in negative ion mode, as well as RNA-peptide complexes being detected. The formation of the noncovalent RNA-peptide complexes showed a correlation with the number of the basic amino acids arginine, lysine and histidine. The strongest influence of these amino acids for complex formation was obtained with arginine. Although different RNA molecules were used with different compositions and secondary structures, no specific effects to complex formation was observed. The comparison of noncovalent complexes with covalent RNA-peptide complexes, which were obtained from ribosomal subunits after cross-linking and enzymatic cleavages, showed that the specific RNA-protein interactions are dependent on the three-dimensional structure of the ribosome and its components. The results of this report indicate that MALDI-MS may be useful for the study of noncovalent interactions, in particular for peptides and RNA.