It has been shown that (+)-cyanidanol-3 ((+)-catechin) is able to stimulate in vitro the cell-mediated immune response specific for hepatitis B surface antigen (HBsAg), and might contribute to the elimination of hepatitis B virus (HBV) during HBV infection. In the present study, the possible action of two of its derivatives, palmitoyl-3-catechin and heptyl-3-catechin, on this type of immunity was investigated by adding the substances to leucocyte migration inhibition tests performed in presence of PPD and HBsAg, with leucocytes from individuals sensitized to these antigens. In normal individuals sensitized to PPD, the addition of palmitoyl-3-catechin and heptyl-3-catechin amplified the inhibition of migration by resp. 7.2% ( p < 0.05). In patients previously infected by HBV and sensitized to HBsAg, the maximum amplification was resp. 12.7% ( p < 0.001) and 7.6% ( p < 0.05). This effect was dose-dependent. These substances did not modify the leucocyte migration measured in the absence of antigen. Palmitoyl-3-catechin and heptyl-3-catechin therefore seem capable of amplifying the cell-mediated immune response. The effect of the two derivatives, which were selected because of their liposolubility, was more pronounced than the effect of (+)-cyanidanol-3. It is thus possible that the two new catechin-derivatives, not yet in therapeutical use, will also stimulate cell-mediated immunity to HBsAg, and that a more marked clinical effect might be expected.