Mouse embryonal carcinoma cell lines that differ in their patterns of expression of the potential oncogene int-2 have been exploited in a structural analysis of the multiple RNA transcripts characteristic of this gene. Ribonuclease protection experiments indicate that four major classes of int-2 RNA initiate at heterogeneous cap sites within two distinct promoter regions, P1 and P2, spanning approximately 50 and 150 bp respectively. The more downstream promoter P2 is located in a region of the DNA that constitutes an intron in RNA transcripts that initiate at the upstream promoter P1. Otherwise, all four RNA structures share the same splice donor and acceptor sites that define the boundaries of the second and third exons. Further complexity arises through usage of two distinct polyadenylation signals, both variants of the normal consensus, that are separated by 1100 bp. Despite these structural variations, the results suggest that all four major classes of RNA encode the same protein product which shows significant homology to the family of heparin-binding proteins typified by basic fibroblast growth factor (FGF).