AbstractIn‐vitro incubations were used to study the effect of intraruminal administration of a mixture of the polyhydric alcohols, arabinitol, xylitol, galactitiol, mannitol and sorbitol, on fermentation pattern and the fate of the polyhydric alcohols. Incubations were carried out with rumen fluid taken from sheep before receiving polyol and after 2 and 3 weeks of intraruminal administration of 2.12 g polyol DM/kg live wt.0.75per day to observe effects of adaptation. Inclusion of polyol in incubations with unadapted rumen fluid had little effect on the volatile fatty acid pattern. However, with adaptation there was a shift in the fermentation pattern in the presence of polyol towards a higher acetate: propionate ratio. The hexitols rapidly disappeared in all the incubations, while the pentitols were more resistant to fermentation. Significantly faster fermentation of arabinitol by rumen fluid from sheep which had received polyol indicated that adaptation had taken place. In the incubations with adapted microbes, xylitol was significantly more resistant to fermentation than arabinitol; after 6 h incubation, approximately half the xylitol and only one fifth of the arabinitol remained unfermented.Analysis of duodenal digesta from adapted sheep which were receiving polyol showed that most of the small amount of pentitol which entered the small intestine did so within 2–3 h of dosing. Despite the apparent resistance of pentitols to rumen fermentation, only 1.0% of the arabinitol and 1.8% of the xylitol in the daily dose entered the small intest