The human gene coding for vasoactive intestinal peptide was recently isolated and shown to contain seven exons. We now demonstrate that an intron-containing precursor RNA can be the major vasoactive intestinal peptide-related RNA in the cell, which is in contrast to most known genes. By RNA blot analysis using a variety of genomic and cDNA-related probes we show that in a human tumor producing vasoactive intestinal peptide, most of the RNA encoding the peptide is of the precursor type. Similar precursor transcripts were found in total rat brain RNA as well. A proof of the identity of the intron-containing RNA, cDNA clones corresponding to this RNA sequence have been isolated.