Chloroplast preparations from Acetabularia mediterranea were shown to consist mainly of small droplets (2–10 μ) containing some cytoplasm and surrounded by a membrane. An analysis was made of the contribution of the cytoplasmic contamination to photosynthetic metabolism. It is concluded that the majority of the photosynthetic metabolism observed takes place in the chloroplasts, but the degree to which it may be influenced by the presence of cytoplasm cannot be determined. Sucrose synthesis takes place in chloroplast preparations, and possibly in chloroplasts themselves, but its subsequent metabolism to monosaccharides or fructosan requires the organization of whole cells. It seems probable that fructosan synthesis and storage is associated with or in the vacuole.