Summary: Small pieces of mouse aorta were cultured in collagen gels, and the formation of capillary-like tubes from the aortic explant was observed under phase-contrast and transmission electron microscopes. Migration of fibroblastic cells from the aortic explant occurred in 2 days. After about 10 days of culture, capillary-like tubes from the aortic explant were formed in the collagen gels. An immunohistochemical study on the collagen gel culture revealed the expression of fibroblast growth factor 2 (FGF-2) near the aortic explant at the active initial stage, with random migration of fibroblastic cells expressing FGF-9. mRNA was isolated from these cultures, and reverse transcription-polymerase chain reaction (RT-PCR) of the cultures revealed the expressions of both FGF-2 and FGF-9. Based on our results, we propose that FGF-9 is also related to angiogenic events.