Introduction: Secondary hyperparathyroidism (sHPT) is one of the most common abnormalities found in patients with chronic kidney disease (CKD). Measurement of serum PTH concentrations is crucial in diagnosis and treatment of sHPT. Different methods of serum PTH measurement may provide diverse results. This may have a significant impact on the therapeutic approach if under-or over-diagnosis of sHPT occurs. The aim of this study was to compare the results of serum PTH concentrations measured with two commonly used methods -chemiluminescence (CHL) and electrochemiluminescence (ECL). Material and methods: Seventy-seven haemodialysis patients with CKD were enrolled into the study. Blood samples were collected before haemodialysis, in the middle of the week. In all patients, serum PTH concentrations were measured using two methods: CHL and ECL. Results: Serum PTH concentration measured with CHL was significantly higher than that assessed with ECL: 455 pg/mL (352-559) pg/mL vs. 383 pg/mL (243-523) pg/mL; p < 0.0001. Six patients from the studied cohort were treated with cinacalcet. In these patients, the serum PTH concentration was also significantly higher when measured with CHL than with ECL: 755 pg/mL (294-1216) pg/mL and 607 pg/mL (199-1015 pg/mL); p = 0.027, respectively). In three cases serum PTH concentration assessed with CHL method exceeded 300 pg/mL, whereas when measured with ECL it was below 300 pg/mL. Lower serum PTH concentrations could give the rationale to lower cinacalcet dose or to stop such treatment. Conclusions:1. Serum PTH concentrations in haemodialysis patients with CKD measured by CHL and ECL methods differ significantly.