Study objective: To examine the hemodynamic and metabolic short-term effects of hypophosphatemia correction in patients with septic shock receiving catecholamine therapy. Design: Prospective, single cohort study. Setting: ICU, university hospital. Patients: Ten patients with septic shock and hypophosphatemia below 2 mg/dL. Interventions: Infusion of glucose-1-phosphate solution (20 mmol of elemental phosphorus) for 60 min. Measurements and results: Hemodynamic, oxygen-derived, acid-base, and electrolyte parameters before and immediately after phosphate infusion. Left ventricular stroke work index increased significantly (22%) from a mean low value of 24 +/- 10 g/m(2) without changes in filling pressures. Systolic arterial pressure improved by 12%. Arterial pH improved slightly but significantly. Ionized calcium level slightly decreased within the normal range values. Other parameters remained unchanged. Conclusions: Severe hypophosphatemia may be considered as a superimposed cause of myocardial depression, inadequate peripheral vasodilatation, and acidosis in septic shock. A rapid correction of hypophosphatemia is well tolerated and may have both myocardial and vascular beneficial effects. The magnitude of the response, however, is variable and unpredictable on the basis of serum phosphorus levels.