Rhodobacter sphaeroides RV cells were cultivated on lactate containing solutions derived from the acidogenesis of source selected municipal solid wastes. Cells were also used for the phototrophic hydrogen evolution using the same substrate. Batch-wise and continuous experiments showed that the acidic aqueous stream obtained from such refuse is quite a good substrate for the growth of R. sphaeroides RV without any integrations. On the contrary, the hydrogen evolution requires external microelements such as iron and, mainly molybdenum. In the presence of these elements, 1-1 chemostats operated at 25 h residence time, T = 30 degrees C, pH = 7.2 and continuous illumination at 10 klux, were able to give 8-10 days of stable hydrogen evolution at rates much higher than artificial substrates containing identical concentration of nutrients (100 vs 35 mi H-2/g dry weight/h). This is probably due to an higher expression of the conventional Mo nitrogenase.