The photosynthetic activity of particles obtained by lysozyme treatment of lyophilized cells from the blue-green alga Anacystis is described. Particles washed once catalyze cyclic photophosphorylation with PMS * and menadion as cofactor at a rate of about 150 and 70 μmoles ATP/h/mg chlorphyll, respectively, a Hill - reaction with ferricyanide coupled to ATP-formation, and pseudocyclic photophosphorylation. The ratio of ATP formed to two electrons transferred is 1 to 3. Repeated washing of the particles removes the phycocyanin without impairment of PMS catalyzed cyclic photophosphorylation, which is not inhibited by DCMU and antimycin and requires 10-3 -m. NH4Cl or 10-5 -m. desaspidin for uncoupling.