This study explored the association between stress-induced hemoconcentration and plasma colloid osmotic pressure, hemodynamic reactivity, and microvascular permeability during a protracted stress task in 26 healthy, young participants. Microvascular permeability was measured during rest using venous congestion plethysmography in a subsample of 13 participants. The task increased hematocrit, colloid osmotic pressure, blood pressure, and heart rate and decreased R-wave to pulse interval. Resting microvascular permeability was not correlated with hemoconcentration. Colloid osmotic pressure and diastolic blood pressure were associated with stress-induced hemoconcentration throughout the task. The association with systolic blood pressure as well as heart rate, however, was more evident during the initial 8min of the task than throughout the total task duration. These findings suggest that factors associated with hemoconcentration vary with task duration.