This article presents AudioGuide, an innovative application for sound synthesis which aims to heighten compositional control of morphology in electronic music. We begin with a discussion of the challenges of managing detail when composing with computers, emphasizing the need for more tools which help the composer address the intricacies of sonic evolution. AudioGuide's approach—using a soundfile as a method for specifying morphological shape—provides a simple yet exacting medium for representing temporal ideas. Using the spectral structure of a soundfile, AudioGuide organizes a user-defined collection of pre-recorded sounds to create a similar morphological contour. Our matching strategy accounts for the spectral content, temporal evolution, and superimposition of sonic elements. We provide two examples which illuminate the capabilities of the algorithm from within a musical context.