Planned for living cell microscopy is the Zeiss LSM 510 confocal/multiphoton microscope, with tunable Ti-sapphire laser. Four detection channels will allow simultaneous acquisition of confocal, multiphoton, and transmitted-light images. And the reduced photodamage afforded by multiphoton optical sectioning will be especially useful for prolonged imaging of sensitive living cells. The microscope will be fitted with two additional components that will allow quantitative imaging of molecules in living cells. A module for fluorescence lifetime imaging with picosecond resolution (SPC-730, Becker and Hickl GmbH) will make it possible to produce images whose intensity is a function of fluorescence decay rather than photon emission per se. This brings to the table an ability to measure subtle alterations in the molecular environment of the fluorophore inside the living cell, facilitating quantitative analysis of protein-protein and protein-ligand binding. The microscope will also be fitted with a detector for fluorescence correlation microscopy, the ConfoCor 2, from Zeiss, which uses an avalanche photo diode array to sensitively measure fluorescence within a tiny (femtoliter) confocal volume positioned at an appropriate location within a living cell. By measuring fluctuations in fluorescence intensity, this technique can be used for quantitative analysis of molecular diffusion and concentration and in molecular binding studies.