Haemodialysis using a bicarbonate concentrate (bicarbonate dialysis) is the treatment modality of choice for correction of metabolic acidosis in chronic renal failure. However, improper ratios of acid and bicarbonate concentrates in dialysis fluid can result in an iatrogenically induced metabolic acidosis. The following report presents a case of acute metabolic acidosis, which resulted from the accidental use of an inappropriate bicarbonate concentrate for haemodialysis treatment. Awareness of the problem and a rapid examination of the dialysis fluid in patients who unexpectedly deteriorate rather than improve with haemodialysis may help in averting potentially severe complications due to errors in the concentrate selection. Conductivity cell devises are not suitable for the control of the acid-base composition of the dialysis fluid (dialysate), therefore, monitoring of the dialysate pH in addition to conductivity should become part of the equipment in haemodialysis machines.