Plasma C1q, C1 esterase inactivator, C4, C3 and C3 proactivator were measured in 20 chronic uremic patients on maintenance hemodialysis, in 10 conservatively treated chronic uremic patients and in 20 healthy volunteers. There was no statistical significant difference between the patient groups in any of the measured complement components. The C1q, C1 esterase inactivator and C4 concentration were found to be the same in the patient and the control groups. The C3 and C3 proactivator levels were equally and significantly lower in both patient groups compared with the healthy volunteers.