The structure, transformation, and bioactivity of single living Schizosaccharomyces pombe cells at the molecular level have been studied in vivo by time- and space-resolved Raman spectroscopy. A time resolution of 100 s and a space resolution of 250 nm have been achieved with the use of a confocal Raman microspectrometer. The space-resolved Raman spectra of living S. pombe cells at different cell cycle stages were recorded in an effort to elucidate the molecular compositions of organelles, including nuclei, cytoplasm, mitochondria, and septa. The time- and space-resolved measurement of the central part of a dividing yeast cell showed continuous spectral evolution from that of the nucleus to those of the cytoplasm and mitochondria and finally to that of the septum, in accordance with the transformation during the cell cycle. A strong Raman band was observed at 1602 cm(-)(1) only when cells were under good nutrient conditions. The effect of a respiration inhibitor, KCN, on a living yeast cell was studied by measuring the Raman spectra of its mitochondria. A sudden disappearance of the 1602 cm(-)(1) band followed by the change in the shape and intensity of the phospholipid bands was observed, indicating a strong relationship between the cell activity and the intensity of this band. We therefore call this band "the Raman spectroscopic signature of life". The Raman mapping of a living yeast cell was also carried out. Not only the distributions of molecular species but also those of active mitochondria in the cell were successfully visualized in vivo.