Glycosylation degree of serum transferrin and the type of its protein variants in patients with cystic fibrosis (CF) were recorded by isoelectric focusing and possible relation to the CFTR genotype, P. aeruginosa infection, respiratory capacity and pancreatic (in)sufficiency was checked. Our results did not confirm some earlier findings of Tf hypoglycosylation in CF, however, we observed significant mean increase (p=0.001) of Tf C2 allele frequency in the patients when compared to controls.