Extracts from either bean chloroplasts or etioplasts stimulate photophosphorylation in partially deficient chloroplast residues. Both extracts contain a latent Ca2+-dependent ATPase but the specific activity of the chloroplast extract is about sevenfold higher. The etioplast ATPase appears to have identical properties to a spinach chloroplast ATPase that has been shown to be a modified coupling factor for photophosphorylation.