Twenty-five patients with post-transfusional C hepatitis have been tested retrospectively by IIIrd generation Recombinant Immuno Blot Assay (RIBA) in order to evaluate long-term anti HCV antibodies dynamics. The test was performed 1, 15, 70 and 140 days after the onset of the disease. Fifteen patients recovered and 10 became chronic. In the 15th day anti C33 and anti C22 were found in 76% of subjects, anti NS5 in 68% and anti C100 in 32%. In the 70th day, 96%, of patients had anti C22, 92% had anti C33 and anti NS5 and 52% showed anti C100. In the 140th day, all patients were positive for anti C33, and C22 and anti NS5, while anti C100 was present in 64%. Five-six years after the acute disease, all chronically progressed patients had a complete antibody pattern by RIBA III, while anti C22 was the only positive persisting antibody, among the recovered patients. Anti C22, anti C33 and anti NS5 shorten the serological "window-phase" during acute hepatitis, but no further improvement in diagnostic precocity seems to be guaranteed by third generation RIBA. The precocious appearance of complete RIBA III pattern during acute hepatitis may represent a herald for a chronic evolution of the disease.