We consider isometric immersions F: M --* h4 between Riemannian manifolds whose higher mean curvature forms [in the sense of the author, Manuscripta Math. 49 (1984), 177-194] are all (covariantly) constant or, equivalently, whose shape operator with respect to each parallel unit normal vector field along any curve in M has constant eigenvalues: As in the hypersurface case we call such immersions isoparametric. Among other results it is proved: Isoparametric surfaces of constant curvature spaces are symmetric, i.e. have parallel second fundamental form. The same is true for isoparametric K/ihlerian hypersurfaces of complex space forms. AMS (MOS) SUBJECT CLASSIFICATIONS: (1980): 53B25, 53A07, 53C42 KEY WORDS: higher mean curvature forms, isoparametric, symmetric submanifolds Geometriae Dedicata 211 (1986), 367-387.