Independent supramolecular nanocarriers can transport pairs of complementary reactants inside living cells in two consecutive incubation steps. After the second internalization step, the nonemissive reactants produce a fluorescent product with the concomitant appearance of intense fluorescence exclusively in the intracellular space. These results demonstrate that supramolecular delivery can be exploited to perform chemical reactions inside target cells and can lead to valuable strategies for the intracellular synthesis of drugs.