Contents of Part B. Introduction and Overview (D.G. Söll). 1. Synthesis and function of modified nucleosides (G.R. Björk, J. Kohli). 2. Biosynthesis and function of queuine and queuosine (H. Kersten, W. Kersten). 3. Codon usage and Q-base modification in Drosophila melanogaster (E. Kubli). 4. Solid phase immunoassay for determining the inosine content in transfer RNA (E.F. Yamasaki, A.A. Wani, R.W. Trewyn). 5. Site directed replacement of nucleotides in the anticodon loop of tRNA: application to the study of inosine biosynthesis in yeast tRNAAla (K.A. Kretz, R.W. Trewyn, G. Keith, H. Grosjean). 6. tRNA and tRNA-like molecules: structural peculiarities and biological recognition (R.L. Joshi, A.-L. Haenni). 7. Mitochondrial tRNAs-structure, modified nucleosides and codon reading patterns (G. Dirheimer, R.P. Martin). 8. The modified nucleotides in ribosomal RNA from man and other eukaryotes (B.E.H. Maden). Modified uridines in the first positions of anticodons of tRNAs and mechanisms of codon recognition (S. Yokoyama, T. Miyazawa). 10. Natural occurring modified nucleosides in DNA (M. Ehrlich, X.-Y. Zhang). Subject Index.