The feasibility of a process for the photoproduction of both H-2 and poly-beta-hydroxybutyrate (PHB)-containing biomass has been tested utilizing semi-continuous cultures of Rhodopseudomonas palustris growing in a tubular system with limiting amounts of fixed nitrogen. A two-stage batch process, consisting in a first period of nitrogen-limited cell growth followed by a second period of cell cultivation under conditions of phosphorus shortage, showed the possibility to separate the H-2 production phase from the PHB accumulation phase, making possible to carry out processes that otherwise would be in competition.