The practice of the Swiss-German artist Dieter Roth is distinguished by his pioneering use, since the early 1960s, of biodegradable materials. This essay examines the development of Roth's practice from Concrete Art to process-oriented and biodegradable work in the context of the reconceptualization of the “concrete” within the global artistic network of Fluxus in the postwar period. Highlighting the challenge Roth's biodegradable work poses to the traditional conceptual limits of the spheres of culture and nature, it argues that the profound transformation of Roth's practice in the early 1960s was rooted in the artist's growing discontent with the idealist and ethical premises of modern art and aesthetics, at the heart of which is the distinction between the human and the nonhuman. In this, Roth's biodegradable works precede later preoccupations with how humans relate to the natural environment, both in early earthworks from the late '60s and in contemporary practice. By examining Roth's biodegradable works in the context of Fluxus, this essay points towards aspects of Fluxus work that remain unexamined, most crucially the role of the natural and the nonhuman in Fluxus critiques of representation.