Confocal fluorescence lifetime imaging microscopy (FLIM) showed the homogeneous distribution of the dyes and the energy transfer across the entire crystals. The FLIM images of crystals loaded with sodium fluorescein (= donor) and sodium resorufin (= acceptor) were obtained by exciting the donor at  = 470 nm and detecting the emission at  = 500-540 nm (= emission from the donor) and at  = 650-700 nm (= emission from the acceptor). Z-scanning of crystals saturated with sodium fluorescein revealed that these guest molecules are distributed across the whole crystal. In accordance with the steady-state emission spectrum, FLIM images of crystals saturated with sodium fluorescein and with different amounts of sodium resorufin showed also the varied degree of energy transfer between this donor -acceptor pair.