Background Patients undergoing chemotherapeutic treatment are currently treated by a concomittent infusion of alizapride and ondansetron. To optimise the procedure and to ensure patients’ safety, the admixture could be prepared in advance by the Centralized Intravenous Additive Service (CIVAS) provided that the stability of the mixture has been proven beforhand to reduce nausea and vomiting. Aim of the study: to evaluate the long-term stability of an admixture of alizapride 0.926 mg/l and ondansetron 0.074 mg/ml in 0.9% sodium chloride polyolefin bags stored at 5 ± 3°C. Material and methods Five polyolefin bags containing 100 ml sodium chloride 0.9% added with 4 ml alizapride (100 mg) and 4 ml ondansetron (8 mg) were prepared in aseptic conditions and stored at 5 ± 3°C for 56 days. Periodically, physical stability tests were performed including: pH measurements, optical density measurements at 350, 410 and 550 nm to track turbidity appearance, visual and microscopical inspections to detect colour changes, precipitation, microaggregates or crystals. The concentrations of the solutions were measured by High Performance Liquid Chromatography coupled with an UV detector. Results There was no change in pH and optical densities during the study period. Visual and microscopical inspections didn’t show any change of colour neither precipitation, microaggregate or crystal. The alizapride and ondansetron concentrations remained stable over the study. Conclusion The admixture of alizapride and ondansetron in 0.9% sodium chloride solution polyolefin bags is physicochemically stable up to 56 days at 5 ± 3°C. These results support the possibility of preparing the solutions in advance by a CIVAS.