H-2 photoproduction by Rhodobacter sphaeroides GL-1 immobilised on polyurethane foam in a continuous flow photobioreactor was shown to occur for prolonged periods. Under optimal conditions (300 W m(-2); dilution rate 0.023 h(-1)) the rate of H-2 production was 0.21 ml h(-1) ml(-1) foam matrix with an efficiency for lactic acid to H-2 conversion of 86%. The duration of the process (35 days of operation) showed no major limitations.