Computer-modulated profile hemodialysis was examined for patients' comfort and fluid-shift. Fifteen patients were studied after two weeks of dialysis with each of the following profiles: A): constant ultrafiltration (UF) and dialysate sodium (138 mmol/l); B): decreasing UF; C): decreasing UF and decreasing high dialysate sodium (starting 10% above serum-sodium, with a gradual reduction to 138 mmol/l in the fourth hour). Patients with a calculated increase of intracellular volume (ICV) during dialysis had more complaints after dialysis than the others. ICV decreased in all patients with low serum-sodium (less than 136 mmol/l) during all profiles, whereas in patients with higher sodium, only profile C led to a decrease of ICV. However, interdialytic weight gain increased about 75% in patients with low serum-sodium under profile C. The sodium profile could help in preventing imbalance without side effects in patients with high sodium.