Films of bacterial poly(3-hydroxyoctanoate) (PHO) (M-n = 85 000) pure or blended with racemic poly[(R,S)-lactic acid] (PLA50) of low molecular weight (M-n = 1100) were prepared by solvent casting techniques and incubated in buffer solutions at 37 degrees C and at different pH. Changes in weight, molecular weight and morphology were recorded during hydrolysis experiments. The PHO hydrolytic degradation process was very slow : after 5 months of degradation, only 0.1% of ester functions were hydrolyzed. In the case of a PHO/PLA50 blend (80/20, w/w), after 1 month, no more PLA50 was present in the film and PHO molecular weight decrease was significantly more important than in the case of pure PHO degradation; the hydrolytic scission of PHO chains was enhanced by the presence of PLA50. Differential scanning calorimetry achieved on PHO/PLA50-blended samples displayed a lack of complete miscibility between both components. In the early stage of ageing, an increase of crystallinity for the different materials was observed in all cases.