Current models for magnetoviscosity suggest that replacing the spherical nanoparticles of a conventional ferrofluid with magnetic nanotubes would lead to a stronger field-induced viscosity enhancement and a much-improved stability against shear thinning - two important parameters for technological exploitation of the magnetoviscous effect. We report the development of positive and negative templating strategies for the synthesis of magnetic nanotubes out of a variety of materials. Our positive template is Tobacco mosaic virus (TMV) - in natural form or genetically engineered to express specific surface chemistries and lengths - which we exploit as a template for the electroless deposition (ELD) of nanosized clusters of nickel and as a scaffold for magnetic particles in a conventional ferrofluid. Our negative templating strategy employs porous anodic aluminum oxide (AAO) as a substrate for the atomic layer deposition (ALD) of a conformal coating of iron oxide, offering precise control over the length and wall thickness of the resulting nanotubes. Both strategies were scaled up to produce the mass quantities of uniform-aspect-ratio nanotubes that are needed for macroscopic ferrofluid volumes. The magnetoviscosity of these ``nanotube ferrofluid{''} samples was studied as a function of applied magnetic field and shear frequency, and a particularly strong effect was found to be induced by viral scaffolding. (C) 2010 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim