Interactions of cells with their chemical microenvironments are critical to many polarized processes, including differentiation, migration, and pathfinding. To investigate such cellular events, tools are required that can rapidly reshape the microscopic chemical landscapes presented to cultured cells. Existing chemical dosing technologies rely on use of pre-fabricated chemical gradients, thus offering static cell-reagent interactions. Such interactions are particularly limiting for studying migration and chemotaxis, during which cells undergo rapid changes in position, morphology, and intracellular signaling. This dissertation describes the use of laminar streams, containing cellular effector molecules, for precise delivery of effectors to selected subcellular regions. In this approach, cells are grown on an ultra-thin polymer membrane that serves as a barrier to an underlying reagent reservoir. By using a tightly-focused pulsed laser beam, micron-diameter pores can be ablated in the membrane upstream of desired subcellular dosing sites. Emerging through these pores are well-defined reagent streams, which dose the targeted regions. Multiple pores can be ablated to allow parallel delivery of effector molecules to an arbitrary number of targets. Importantly, both the directionality and the composition of the reagent streams can be changed on-the-fly under a second to present dynamically changing chemical signals to cells undergoing migration. These methods are applied to study the chemotactic responses of neutrophil precursor cells. The subcellular localization of the chemical signals emerging through pores is found to influence the morphological evolution of these motile cells as they polarize and migrate in response to rapidly altered effector gradients. / text