We developed a technique for spatiotemporally precise control of downstream signaling of receptor tyrosine kinase by ultraviolet light irradiation of caged fluorescein-based receptor ligands in cells expressing an antifluorescein antibody-receptor tyrosine kinase chimera. Light-driven ligand uncaging specifically elicited receptor phosphorylation and calcium mobilization in irradiated cells. This technique may be useful for detailed studies of the physiological roles and dynamics of receptor tyrosine kinase signaling.