When Saccharomyces cerevisiae cells were inoculated at low density (1 . 10(3)-1.5 . 10(5) cells [g gel](-1)] in alginate gel beads and cylinders, cells grew in the form of distinct microcolonies throughout the gel matrix. Alginate gel bends and cylinders, formed by external gelation with Ca2+, gave rise to microcolonies which became elongated and lens-shaped with their major axes aligned with the gel surface. The aspect ratio (major axis/minor axis length) of the microcolonies and the local concentration of alginate increased with increasing distance from the center of the gel particles. In contrast, spherical microcolonies were observed in alginate cylinders formed by internal gelation and no significant local concentration gradients of alginate were detected in these gels. Nonspherical microcolonies were also observed in carrageenan gel bends. However, the colonies were irregularly shaped, and their major awes demonstrated no preferential alignment.