This study provides a comparative evaluation of the losses of free amino acids which take place in the various artificial substitutive therapies for chronic uraemia (conventional haemodialysis, haemofiltration, haemoperfusion, continuous ambulatory peritoneal dialysis, intermittent peritoneal dialysis). The highest loss was found during haemofiltration sessions, the lowest in continuous ambulatory peritoneal dialysis. The differing loss rates do not influence patients' plasma amino acid patterns either in the short or in the long term (up to 12 months). Moreover, no currently available artificial therapy can correct the basic uraemia-related alterations of plasma amino acid patterns.