Recent n.m.r. studies of intact red cells are described. With 1 H n.m.r. the normal high resolution spectra of red cells, even at high fields, are relatively uninformative because the very large number of resonances from the cells merge into a broad envelope. If a simple 90- τ - 180° spin echo pulse sequence is used, however, many resonances can be resolved. These include signals from haemoglobin histidines, glutathione, lactate and pyruvate. 13 C and 31 P signals have also been seen with a spectrometer converted to observe these nuclei essentially simultaneously. N.m.r. is well suited to monitor the time course of events after a perturbation of the cell system. Lactate increase, glutathione recovery after oxidation and alkylation of glutathione by iodoacetate can all be observed directly in red cell suspensions by means of 1 H spin echo n.m.r. This method has also been used to measure isotope exchange ( 1 H - 2 H) of lactate and of pyruvate at both the C-3 and the C-2 positions, and some of these exchange rates can be interpreted in terms of the activity of specific enzymes in the cells. 1 H spin echo n.m.r. has also been used to obtain information about the transport rates of small molecules into cells. By means of the 13 C / 31 P spectrometer and [ 13 C-1] glucose, the 13 C enrichment of 2,3-diphosphoglycerate (2,3-DPG) can be monitored at the same time as the levels of 2,3-DPG, ATP and inorganic phosphate are observed by 31 P n.m.r.