An analysis of the compartmentation and fluxes of inorganic phosphate in isolated cladophyll cells from Asparagus officinalis was made in parallel with an ultrastructural study. The elution pattern of labelled inorganic phosphate (which indicates that the asparagus cells are behaving as a system of three compartments in series) was used to quantify the fluxes between the vacuole, cytoplasm and free space. A relaxation time of 198 min was calculated for inorganic phosphate exchange between the vacuole and cytoplasm. It is, therefore, suggested that the vacuole serves to buffer the cytoplasmic inorganic phosphate concentration in the long term. However, in the short term, exchange with the vacuole will not appreciably affect the cytoplasmic inorganic phosphate concentration and thus the partitioning of photosynthetically fixed carbon.