The degradability of starch fiom various feedstuffs was investigated in vitro by incubation of 500-mg amounts in 50 ml of a 3:1 rumen fluidlbuffer solution at 39°C for 6 h. The rumen fluid was obtained from one of three cows fed on hay or hay and concentrate. The degree of degradation a f e r 6 h incubation varied strongly for the 23 feedstuffs investigated. The degradation of starch fiom the same feedstuff in rumen fluid from a hayged cow was significantly lower than in rumen fluid from a concentrate-fed cow. I t seemed that differences in degradability between feedstuffs were not determined by the ration of the donor cow, but merely by the properties of the starch. Processed feedstufs showed a higher degradation of their starch than the unprocessed feedstufs, independent of the ration of the donor cow. Particle size influenced degradation, but not of the starch of tapioca meal. A fairly constant ranking in degradability between the various @edstuffs was found. Fermentation of mixtures of jkedstufs showed about the same rate of degradation as found for the single products. Only when great differences in the degree of degradability existed was the degradation of the total starch enhanced. The time of collection of rumen fluid strongly influenced the in-vitro degradation of starch.