OBJECTIVE Collateral vessels restore only about 40% of the maximum dilatory reserve after femoral artery occlusion, whereas complete normalization is reached by increased fluid shear stress (FSS). We studied the role of known potent angiogenic growth factors (separately or in combination) in arteriogenesis by determining their expression in FSS-stimulated collaterals and close-to-collateral infusion of growth factor peptides in a rabbit model of femoral artery occlusion. METHODS Values of maximum collateral conductance (C(max)) and post mortem angiograms were compared to those achievable by high FSS. mRNA levels of growth factor ligands and receptors were determined in FSS-stimulated collaterals. RESULTS Seven days after vessel occlusion, FSS-stimulated legs showed a C(max) not significantly different from that of not occluded femoral arteries. Arteriogenesis was significantly less enhanced after growth factor treatment (MCP-1 86%, Ad5.1-FGF-4 75%, bFGF 72%, PDGF 64%, VEGF 50% of C(max) after FSS stimulation). RT-PCR showed no differential expression of FGF receptors, but an up-regulation of VEGF-receptor-2. CONCLUSIONS The most potent known angiogenic growth factors at high pharmacological doses reach only a fraction of the maximum conductance obtained by high FSS. Arteriogenesis differs from angiogenesis, so the main focus to markedly improve arteriogenesis should be put on the underlying mechanisms of shear stress.