Murine immortal fibroblasts express a form of vascular endothelial growth factor (VEGF) that was cloned, characterized and named VEGF 115. It differs from VEGF 120 by 37 amino acids at the carboxyl terminus. VEGF 115-specific sequence reacted to a single transcript in mouse tissues. Reverse transcription-polymerase chain reaction was performed in mouse tissues and in fibroblasts of normal and immortal divisional phenotypes. The data from mouse tissues suggested that VEGF 115 is not a tissue-specific isoform of VEGF 120, whereas a functional relevance with immortalization is indicated from the latter. The novel cDNA was expressed in Escherichia coli, and the His-tagged VEGF 115 (17.2 kDa) thus obtained was recognized by anti-VEGF antibody. A mammalian expression plasmid, pCMVneo+, encoding for VEGF 115 was transfected to NIH 3T3 cells, and the conditioned medium of stable transfectants was found to have fibroblast growth factor-replacing activity for human umbilical vein endothelial cells. Two independent genomic P1 clonings with primers specific for VEGF 164 and VEGF 115, respectively, resulted in isolation of identical P1 clones. We analyzed these three P1 clones on Southern blots with common and specific probes for VEGF 164 and VEGF 115. The results support the hypothesis that VEGF 115 is a new alternatively spliced form of mouse VEGF.