To see if the cluster of metabolic and haemodynamic variables defined as comprising Syndrome X varied as a function of urinary albumin excretion (UAE) rate in a healthy population. A cross-sectional, population-based study. A factory in Italy. Two hundred and twenty-five healthy volunteers, 115 men and 110 women. OUTCOME MEASURES. Measurements were made of the plasma glucose and insulin responses to oral glucose, fasting triglyceride (TG) and high density lipoprotein (HDL)-cholesterol concentrations, blood pressure, and UAE rates. Only five of the 225 volunteers had micro-albuminuria, defined as a UAE rate > 2 micrograms min-1, and the UAE rate was < 5 micrograms min-1 in 80% of the volunteers. Significant variations in the metabolic and haemodynamic variables measured were not associated with any differences in UAE. Finally, significant relationships were found between various measures of plasma insulin concentration and plasma glucose response to oral glucose, plasma TG and HDL-cholesterol concentrations, and mean arterial blood pressure, independent of variations in age, body mass index, ratio of waist-to-hip girth, and UAE rates. The widespread variability in plasma glucose and insulin responses, plasma TG and HDL-cholesterol concentrations, and blood pressure that are seen in the population at large cannot be attributed to variations in UAE rate.