This study was designed to investigate the acute effects of balanced versus unbalanced colloid resuscitation on renal macrocirculatory and microcirculatory perfusions during lipopolysaccharide-induced endotoxemic shock in rats. We tested the hypothesis that balanced colloid resuscitation would be better for the kidney than unbalanced colloid resuscitation. Shock was induced by lipopolysaccharide (10 mg/kg i.v. over 30 min). When mean arterial pressure (MAP) was decreased to 40 mmHg, fluid resuscitation was started with either hydroxyethyl starch (HES130/0.42) dissolved in saline (HES-NaCl) as an unbalanced colloid solution or HES130/0.42 dissolved in Ringer's acetate (HES-RA) as a balanced colloid solution. Microvascular perfusion in the renal cortex was monitored using laser speckle imaging, and in addition, systemic hemodynamics, renal artery blood flow (RBF), and plasma ion levels were measured. Shock decreased MAP, led to anuria, and worsened all other parameters. Hydroxyethyl starch-NaCl improved MAP (P > 0.05) but did not improve RBF (P > 0.05), metabolic acidosis (P > 0.05), and plasma ion levels (P > 0.05). Hydroxyethyl starch-RA improved MAP (P < 0.05), RBF (P < 0.05), and renal microvascular perfusion (P < 0.05), but did not improve metabolic acidosis (P 9 0.05) and plasma ion levels (P > 0.05). Both HES-NaCl and HES-RA treatment could normalize creatinine clearance but not fractional sodium excretion. In endotoxemic rats, balanced colloid (HES) resuscitation was shown to be superior to unbalanced colloid resuscitation in terms of improvement of renal macrovascular and microvascular perfusions. However, whether this results in improved renal function in the long term warrants further study.