We study the relationship between different margins of information technology (IT) use and vertical integration using plant-level data from the U.S. Census of Manufactures. Focusing on the short-run decision of whether to allocate production output to downstream plants within the same firm or to external customers, we find that customer-focused IT, by itself, has surprisingly little impact. In contrast, adoption of upstream supplier-focused IT at a plant is associated with a significant decline in downstream vertical integration. However, the greatest decline in within-firm transfers occurs when supplier- and customer-facing IT are adopted together, suggesting the presence of complementarities in supply chain technology adoption. These results are consistent with the view that, by reducing external coordination costs, IT investments promote a decline in plant-level vertical integration, but only when those investments are made jointly with both suppliers and customers. Our results provide less support for the view that IT investments led to a decline in vertical integration by lowering transactions risks.