['Marked variability exists in coronary artery collaterals in patients with ischemic heart disease. Multiple factors are thought to play a role in collateral development; however, the contribution of hypoxia inducible factor-1alpha (HIF-1alpha), which is a transcriptional activator that functions as a master regulator of oxygen homeostasis, is not completely clear. It could play an important role in modulating collateral development.', 'The objective of this study is to investigate the changes and significance of expression of HIF-1alpha in patients with coronary artery collaterals.', 'Collateral vessels were determined in 98 patients with >or=70% narrowing of at least one coronary artery without earlier revascularization, 42 patients with coronary artery collaterals and 56 patients with no coronary artery collaterals. Extent of collaterals was expressed as scores according to the Rentrop scoring system. Another 50 cases with normal coronary arteries were selected as control. The levels of HIF-1alpha protein expression in monocyte and lymphocyte in the participants were tested by immunohistochemistry (IHC) and western blot; mRNA levels were measured using reverse transcriptase PCR technique.', 'Compared with the control with normal coronary artery, the patients had higher expression of HIF-1alpha protein tested by IHC and western blot (52.6+/-10.2 vs. 13.7+/-6.2 by IHC, 50.8+/-4.5 vs. 6.5+/-1.8 by western blot); furthermore, significantly higher HIF-1alpha expression was observed in patients with collaterals compared with patients with no collaterals (81.5+/-11.8 vs. 20.7+/-9.4 by IHC; 87.2+/-6.5 vs. 9.5+/-1.4 by western blot). On the transcriptional levels of HIF-1alpha, the result was the same as the protein, there was significant difference of HIF-1alpha between the three groups. The patients with collaterals were the highest (127.3+/-23.9), followed by patients with no collaterals (35.7+/-12.3), and the control were the lowest (23.5+/-9.3). A highly positive correlation was observed between the expression/transcription of HIF-1alpha and collateral score (P<0.01, IHC: r1=0.78, reverse transcriptase PCR: r2=0.69, western blot: r3=0.84).'] Does hypoxia-inducible factor-1alpha induce the coronary collaterals for coronary artery disease?