Microalbuminuria, considered a marker for systemic vascular disease, is a significant predictor of increased risk for cardiovascular morbidity and mortality in the general population. The relationship between microalbuminuria and cardiovascular disease is unknown. The aim of this study is to examine the association between microalbuminuria and coronary collateral vessel (CCV) development in nondiabetic and nonhypertensive patients with unstable coronary artery disease (USCAD). One hundred and six patients that had USCAD without hypertension and diabetes participated in the study. Microalbuminuria was assessed by radioimmunoassay in 24-h urine collections performed on the first day, and coronary angiography was performed 2-4 days after admissions. In total, 26 patients (mean age 56+/-14 years) had the criteria of the microalbuminuria group and 80 patients with normoalbuminuria (mean age 59+/-11 years), who had one or more diseased vessels with 80% or more stenosis, were included in the control group. The CCVs are graded according to the Rentrop scoring system and a Rentrop grade >or=1 was accepted as CCV development. CCV development was detected in eight (23%) of 26 patients in the microalbuminuria group and in 53 (74%) of 80 patients in the normoalbuminuria group. CCV development in the patients in the normoalbuminuria group was significantly different from that of the patients in the microalbuminuria group (r = -0.15, P = 0.006). In conclusion, these findings suggest that CCV development is poorer in the microalbuminuria group than the normoalbuminuria group. This study shows that in patients with USCAD, microalbuminuria, which is related to systemic vascular disease, affects CCV development negatively.