Herpes simplex virus 1 (HSV-1) mutants selected in Vero cells either for resistance to plaque development inhibition (PDI) (P1, P2 and P3) or for resistance to neutralization (N1, N2, and N3) against an anti-glycoprotein D (gD) monoclonal antibody (mAb) were characterized both in Vero and BHK cells. In Vero cells P mutants were completely resistant to PDI, while N mutants showed from moderate to good resistance. In BHK cells P mutants lost their resistance to PDI, while N mutants became fully resistant. Cell type influenced the plaque size of the mutants as well. In Vero cells P mutant plaques were larger, and N mutant plaques smaller than wild type virus plaques. In BHK cells all plaques were comparable. With one exception (N2 in BHK) resistance to neutralization could be clearly appreciated at high but not at low mAb:virus particles ratio. For most of the mutants the neutralization values remained approximately the same in Vero and BHK cells. P2 and N2 mutants were more resistant to neutralization in BHK than in Vero cells. However, only for N2 mutant did the change in neutralization resistance go in the same direction as the change in PDI resistance. The results show that it is possible to dissociate the neutralizing and the PDI activities of a mAb and that the sensitivity of a virus to plaque inhibition by an anti-gD mAb is cell-type dependent.