Plasma fibrinogen is a well-known predictor of cardiovascular disturbances, and C-reactive protein (CRP) is associated with elevated causes of myocardial infarction and sudden cardiac death. That is the reason to look for the causes of increased CRP levels in CRF and haemodialysis (HD). The study tries to find whether interleukin-6 (IL-6) is a consistent factor for CRP elevation in CRF and/or in HD patients, when a dialysis-induced IL-6 synthesis may occur, as IL-6 has been claimed as a responsible factor for production of some acute phase proteins like CRP. CRP [enzyme-linked immunosorbent assay (ELISA) technique, limit 0.1 µg/L], IL-6 (ELISA, Medgenix, Brussels, Belgium), and fibrinogen (photometric technique) were tested in 45 stable predialytic CRF patients (mean age 48 ± 7 years) and in 50 stable HD patients (mean age 62 ± 15). In CRF patients, a positive correlation was found between plasma fibrinogen (mean 356 ± 167 mg/dL) and CRP (r = 0.51, p < 0.01) and between fibrinogen and proteinuria (r = 0.32, p < 0.01), but no correlation was found between CRP and IL-6. In HD patients, a high positive correlation was registered between CRP (mean 6.93 ± 5.88 mg/L) and IL-6 (mean 9.4 ± 10.6 pg/mL) (r = 0.84, p < 0.001) and between CRP and fibrinogen (mean 325 ± 110 mg/dL) (r = 0.59, p < 0.001). The study suggests that, in HD patients, one of the factors stimulating hepatic production of CRP is probably IL-6, which is synthesized by the dialysis-related, activated macrophages. In predialytic patients, the bacterial products in dialysate and their effect on macrophages are absent and there is no correlation between CRP and IL-6.