Summary: The familiar procedure of adding white noise to deterministic systems of equations may not be appropriate or even possible in some modelling problems arising in the biological sciences. Although some mathematical handle on indeterminant factors (i.e. ``noise'') may be necessary, sometimes the probabilistic requirements involved cannot be rigorously verified for the data set at hand. As an alternative, we discuss here the modelling utility of fuzzy differential inclusions associated with given systems of nonlinear ODE's. We give concrete examples and give account of the conservative stochastic mechanics of \textit{E. Nelson} [see ``Quantum fluctuations.'' (1985; Zbl 0563.60001)] applied to growth of a dimorphic clone, and its fuzzy differential inclusion analogue.