Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005, India E-mail : govil@tifr.res.in Cells are the basic units of living systems. The interior of cells is separated from the extra-cellular medium by semi-permeable barriers (membranes), which separate the inside from the outside of the cells. Membranes allow passage from inside to outside of the cells and vice-versa in a highly selective manner. In this paper, we have illustrated how drugs change the permeability of cell membranes, and how this information can be used for designing novel drug molecules. Studies on NMR of intact cells have been illustrated with a particular cellular system, spermatozoa. It has been shown how NMR can provide information on the bioenergetics of intact and alive cells. Studies on body tissues can be conducted using solid-state NMR techniques. Such studies allow learning of the chemical processes that take place in living systems, ranging from biological molecules to living systems.