Mesophyll protoplasts of tobacco (Nicotiana tabacum L. cv. Xanthi) were evacuolated by centrifugation in a density gradient. Evacuolation resulted in the quantitative loss of vacuolar hydrolytic activities. The evacuolated miniprotoplasts were cultivated under different conditions, and the regeneration of the central vacuole was investigated by light and electron microscopy as well as by the determination of activities of vacuolar marker enzymes. Vacuoles and hydrolytic activities, as well as cell wall material reappeared faster when the cells were cultivated at low osmotic strength. A newly synthesized tonoplast polypeptide could be detected using a polyspecific serum raised against tonoplast proteins of barley (Hordeum vulgare L.). Both vacuolar proton pumps, the ATPase as well as the pyrophosphatase appear to be newly synthesized during the regeneration of the vacuole.