Fibroblast growth factors (FGF) and their specific receptors (FGFR) have diverse roles, including induction of proliferation in smooth muscle cells which contributes to restenosis after coronary artery balloon angioplasty. The relative levels of expression of the four major types of FGFR were studied in 13 different human arterial smooth muscle cell isolates. Cell lines were established by the explant technique from intima/media tissue samples obtained from patients undergoing either coronary artery bypass surgery or cardiac transplantation procedures. Expression of FGFR isoforms was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) using primers for the conserved tyrosine kinase (TK) domain followed by Southern blotting with TK insert probes unique to each isoform. The data indicate that FGFR I is the major form of FGF receptor mRNA expressed by proliferating human arterial smooth muscle cells. This strongly suggests that it is this type of FGFR that mediates the signal transduction cascade associated with mitogenesis in proliferating human smooth muscle cells.