The amount of copies of HCV-RNA and count of CD8(+) lymphocytes was retrospectively evaluated in 326 patients: sampling was performed in basal condition, during treatment with alpha-IFN (n=232) and post-treatment follow-up, and at the same time points in untreated patients (n=94). In the treated group the difference between CD8(+) lymphocytes in the patients successfully treated (n=65) and those with an unfavourable outcome (n=176) is statistically significant (898+/-172 vs., 440+/-176 CD8(+) lymphocytes per mm(3) P<0.005 ANOVA). Also, in the untreated patients the average count of CD8(+) cells is statistically higher in patients with a favourable outcome (P<0.01 ANOVA). The present data show that the count of CD8(+) lymphocyte is of clinical value in order to predict the outcome of HCV infection and may be used together with the viral load and genotype, already established predictors.