We compared hemorheological parameters in 42 male patients with acute myocardial infarction (AMI), with (n = 22) or without (n = 20) ST-segment elevation and in 20 controls. Plasma and blood viscosity (cP), plasma protein (g/dL) and fibrinogen (mg/dL) concentrations, red (10(6)/mu L) and white (10(3)/mu L) blood cell counts, hemoglobin concentration (g/dL), and hematocrit (%) were compared. Plasma viscosity was significantly higher in patients with AMI with (P = .012) and without (P = .046) ST-segment elevation than in controls. Patients with AMI with and without ST-segment elevation had significantly lower albumin (P = .002 and P = .009) and globulin (P = .001 and P = .007) concentrations, red blood cell counts (P = .0001 and P = .004), and hematocrit (P = .014 and P = .040) and significantly higher fibrinogen concentrations (P = .0001 and P = .001) than controls. These findings suggest that AMI in males is associated with increased plasma viscosity and fibrinogen concentrations and with decreased albumin and globulin concentrations, erythrocyte count, and hematocrit, regardless of ST-segment elevation.