To determine whether microtubules are linked to intracellular transport in absorptive cells of the proximal intestine, quantitative ultrastructural studies were carried out in which microtubule distribution and content were determined in cells from fasting and fed animals. Rats were given a 1-h meal of standard chow, and tissue was taken from the mid-jejunum before, 1/2 h, and 6 h after the meal. The microtubule content of apical, Golgi, and basal regions of cells was quantitated by point-counting stereology. The results show) that microtubules are localized in intracellular regions of enterocytes (apical and Golgi areas) previously shown to be associated with lipid transport, and that the microtubule content within apical and Golgi regions is significantly (P less than 0.01) reduced during transport of foodstuffs. To determine the effect of inhibition of microtubule assembly on transport, colchicine or vinblastine sulfate was administered to postabsorptive rats, and the lipid and microtubule content of enterocytes determined 1 and 3 h later. After treatment with these agents, lipid was found to accumulate in apical regions of the cells; this event was associated with a significant reduction in microtubule content. In conclusion, the regional distribution of microtubules in enterocytes, the decrease in assembled microtubules after a fat-containing meal, and the accumulation of lipid after the administration of antimicrotubule agents suggest that microtubules are related to lipid transport in enterocytes.