RRF-3 is one of the four putative RNA-directed RNA polymerases (RdRPs) in C. elegans and plays a major role in endogenous synthesis of siRNAs. By deep sequencing of mRNA tags (mRNA-seq) from N2 worms and from worms with mutational backgrounds, at different stages, we found that the annotated seventh exon of rrf-3 contains an intron. The position of the intron is chrII: 8165255-8165300 (WS190 version of the C. elegans genome), and it is 45 bp long (Figure 1). The 5′ end of the intron starts with GTATATTCTA and the 3′ ends with AAATATTCAG. The intron does not change the reading frame and shortens the protein by 15 amino acids.