Fibroblasts of the periodontal ligament (PDL) of the mouse exhibit a high degree of cytoplasmic and functional polarity. This polarity is dependent upon an elaborate system of microtubules. The location of the microtubular arrays and the observed effects of colchicine administration suggest that microtubules play an important role in maintaining the organization of the Golgi complex and its functional relationship to the rough endoplasmic reticulum. Smooth-walled intermediate vesicles, apparently derived from the rough endoplasmic reticulum, are aligned along microtubules at the immature face of the Golgi apparatus, and mature secretory granules are closely related to microtubules at the mature face of the Golgi apparatus. In distal cell processes the granules are closely parallel to microtubules and on occasion bridge-like attachments from granules to microtubules were noted. This relationship of secretory granules to microtubules, the lack of granule storage, and the effects of colchicine on granule secretion suggests that microtubules are part of a mechanism for collagen granule translocation from the Golgi complex to the cell periphery.