Background/Aims: Intensive haemodialysis (HD) sometimes causes hypophosphataemia, but phosphate-containing dialysate is not readily available. We examined the effectiveness of extemporaneously producing a phosphate-rich dialysate for use in HD. Methods: Incremental volumes of Fleet® were added to acid concentrate and predicted to deliver dialysate phosphate concentrations of 0.19–1.1 mmol/l, following mixture with ultrapure water and base concentrate by the HD machine. Results: The achieved concentrations were close to predicted values (p = 0.77) and remained stable throughout an 8-hour ‘treatment’ time (p = 0.99). The dialysate phosphate concentration had a linear relationship with the Fleet® volume added, defined by the regression equation y = 172.79 x – 1.47 (R² = 0.99, r = 0.99, p = 0.003). The dialysate pH, calcium, magnesium and bicarbonate concentrations did not change over the study period (p = 0.28–0.99). Microscopic analysis under polarised light showed no evidence of crystal formation. Conclusion: The study validates a simple, reliable and cost-effective protocol for phosphate supplementation in conventional and extended HD.