Chronic kidney disease causes permanent kidney damage and is treated with dialysis. Dialysis is a blood purification technique which removes unwanted molecules and adds necessary substances through a semi-permeable membrane of a haemodialyser. Haemodialysis uses diffusion as its mechanism of action, whereas haemodiafiltration uses ultrafiltration as well as diffusion. Dialysis patients are exposed to 15000 to 20000 L of dialysis fluid per year and are therefore at risk for altered concentrations of essential and toxic elements. We wanted to see if dialysis patients have lower concentrations of essential elements (copper, zinc, chromium, molybdenum and selenium in plasma and manganese in blood) and higher concentrations of toxic elements (aluminium, nickel in plasma and arsenic, cadmium, lead and mercury in blood) compared to the control group of healthy volunteers. Additionally, we wanted to determine if the volume of residual diuresis of dialysis patients is associated with lower concentrations of elements, primarily eliminated by kidneys; if the duration of the dialysis treatment is associated with lower concentrations of essential elements and higher concentrations of toxic elements; and whether dialysis patients treated with haemodiafiltration have lower concentrations of essential elements and higher concentrations of toxic elements as opposed to patients treated with haemodialysis. Samples of plasma and blood were analysed with inductively coupled plasma mass spectrometry. Our results regarding essential elements show that dialysis patients had decreased level of copper (743,6 μg/L; 878,8 μg/L), zinc (634,7 μg/L; 769,1 μg/L) and selenium (64,81 μg/L; 89,21 μg/L) as well as increased levels of chromium (2,2 μg/L; 0,28 μg/L), molybdenum (4,6 μg/L; 0,81 μg/L) and manganese (9,38 μg/L; 7,65 μg/L) in comparison with the control group. Compared with the control group, dialysis patients showed increased levels of aluminium (2,83 μg/L; 1,73 μg/L), cadmium (1,27 μg/L; 0,35 μg/L), nickel (2,06 μg/L; 0,33 μg/L) and lead (74,33 μg/L; 18,42 μg/L), decreased level of mercury (0,47 μg/L; 1,27 μg/L), whereas arsenic level showed no significant difference between the groups. We found decreased level of chromium, nickel, cadmium and lead in dialysis patients with greater residual diuresis. The duration of dialysis treatment was associated with higher level of copper and lead, and lower level of mercury. Haemodiafiltration patients had increased level of nickel and decreased level of arsenic, compared with haemodialysis patients. In the future it would be useful to determine essential and toxic element concentrations after a dialysis session, as well as in fresh and used dialysis fluids, which would give us a much clearer picture of the effect of dialysis treatment on trace element levels.