Fe-0.8C-Co alloys have been unidirectionally transformed by translation through a temperature gradient which establishes a single interface between the austenite and pearlite phases. A comparison between the temperature gradient calculated to maintain a single planar interface by preventing nucleation ahead of the interface and that actually required in the experiment led to the conclusion that the temperature gradient must retard the nucleation of pearlite. The relationship between interface morphology and the resultant pearlitic microstructure was examined, and comparisons made with more familiar pearlite structures produced by conventional isothermal heat treatments. The degree of alignment of the pearlite lamellae was analyzed metallographically and found to be predominantly within 12 deg of the growth direction. A detailed analysis of interlamellar spacing measurements as a function of growth velocity established that pearlite can possess a wide range of interlamellar spacings at any constant growth velocity and that this range seems to be dependent on growth velocity.