Objective: Physiological bicarbonate/lactate-based solutions may correct acidosis in a better way than standard lactate-based solutions. In this study, a new 25 mmol/L bicarbonate/10 mmol/L lactate peritoneal dialysis (PD) solution was compared with a standard 35 mmol/L lactate solution. Design: This was a prospective open label study. All patients had a 2-week baseline period using the standard lactate solution, followed by 8 weeks on the bicarbonate/lactate solution and 2 weeks on the lactate-based solution. Setting: Four Danish and four Spanish nephrology centers. Patients: 40 well-dialyzed (creatinine clearance > 55 L/week/1.73 m2 body surface area) patients on continuous ambulatory PD. Interventions: Blood samples were taken for biochemistry (including venous blood gases) at week -2, day 1, weeks 2, 4, and 8, and at follow-up. A physical examination, a peritoneal equilibration test (PET), and quality of life (K/DQOL), ultrafiltration, and adequacy assessments were performed at baseline and at week 8. Vital signs and other safety parameters were followed at each visit. Extraneal (Baxter Healthcare, Castlebar, Ireland) was used by all patients for the long dwell. Main outcome measure: Effect on the venous plasma bicarbonate level. Results: Venous plasma bicarbonate levels rose from 24.4 mmol/L when patients were on the pure lactate to 26.1 mmol/L when using the bicarbonate/lactate solution (p < 0.001). When patients were using the bicarbonate/lactate solution, 66% of values were maintained within the various normal range of 24-30 mmol/L, versus 46.2% when patients were on the pure lactate solution (p < 0.001). There were no adverse findings with respect to clinical symptoms, vital signs, or physical examination. The PET and adequacy, ultrafiltration, and K/DQOL assessment results were unchanged. Conclusions: The new 25 mmol/L bicarbonate/10 mmol/L lactate solution provided better correction of acidosis than an equivalent 35 mmol/L standard lactate solution, without any safety issues.