Many nucleotides in rRNAs are modified. We devised a method to locate 2'-O-methyl nucleotide residues using a conventional DNA sequencer. We found 38 2'-O-methyl nucleotides in the 26S rRNA of Caenorhabditis elegans using this method. Fourteen of the 38 residues are conserved in both human and yeast rRNAs and 14 residues are conserved in either human or yeast rRNA. The remaining 10 nucleotides are uniquely methylated in C elegans 26S rRNA. We searched the C elegans genomic sequence for small nucleolar RNAs (snoRNAs), which guide the methylation of ribose residues, and predicted 18 snoRNA sequences that are expected to guide the methylation of some of these nucleotide residues. (C) 2002 Elsevier Science (USA). All rights reserved.