Through detailed measurements of the exchange-bias behavior, we have demonstrated that an antiferromagnetic interfacial exchange coupling exists in epitaxial bilayers of the two ferromagnets La0.67Sr0.33MnO3 and SrRuO3. The bilayers were grown on SrTiO3 substrates by pulsed laser deposition with atomic layer control. By field cooling, or by applying a low-temperature pinning field, the bilayers exhibit exchange bias, with the magnetization loops shifted from zero field by the exchange field HE. In the case of field cooling, we find that both the magnitude and sign of exchange field depend on cooling field, consistent with antiferromagnetic interfacial exchange. The coercivity is maximum near the cooling fields that produce zero exchange field.