In 23 patients with chronic renal failure (CRF), 23 patients on chronic intermittent hemodialysis treatment (DP), 22 patients after renal transplantation (RT) and 40 normal persons (NP), Biotin plasma levels and the urinary excretion were analysed and compared to the dietary Biotin intake. Unsupplemented DP had lower intake of Biotin than the CRF, RT, NP and DP with supplementation. DP excreted only 1.6-6.3% of the daily intake as compared to 39.7% in NP, 27.6% in CRF and 24.3% in RT. In unsupplemented DP patients, Biotin plasma levels were elevated by 4 times and in supplemented patients by 6 times compared to NP. During hemodialysis treatment, the Biotin plasma level dropped by about 30% in DP with and by 33% in DP without vitamine supplementation. However, after 44 hours, the initial concentration was reached again in those receiving vitamine supplementation (99% of basal level) and in DP without substitution (97% of basal level). Only in male DP significantly higher Biotin plasma levels before HD were detected irrespective of the supplementation dose as compared to female patients (30 micrograms and 300 micrograms Biotin after each dialysis session). Biotin plasma concentration did not vary with respect to the underlying renal disease, the serum creatinine concentration and the length and frequency of dialysis treatment, including the type of dialyzer (low- vs high flux) used and the blood flow rate (QB 180-260 vs 270-280 vs 300 ml/min). There were no major effects of the age of the patients (< 60 years vs > 60 years), the BMI, nicotine abuse, or alcohol intake on Biotin blood concentration. Our results showed normal Biotin plasma levels which reflect a normal functional status and exclude a functional deficit, therefore there is no reason for a regular Biotin supplementation in patients with chronic renal failure.