Roughage feeds obtained and preserved from meadows infested with toxic plants present a health risk for herbivore livestock. In this context, it is of interest whether toxic alkaloids from autumn crocus (Colchicum autumnale) or ragwort species (Jacobaea/Senecio spp.) can be degraded to an acceptable level during the ensiling process. Fresh autumn crocus plants were incorporated into grass silage bales of 1 m diameter from the region of the Austrian Vienna Woods. After 18-43 weeks, the leaves were recovered from the bales and dried and their colchicine content was analysed. Leaf pieces of autumn crocus were conspicuous and could be easily retrieved from the silage. Alkaloid loss of leaves during ensiling was very variable, ranging from zero to about 20-30% and to 57% in one of eight cases. Marsh ragwort (Jacobaeaaquatica), containing toxic pyrrolizidine alkaloids, was incorporated into two grass silage bales from the Austrian Waldviertel region. After 29 weeks, the toxic plants were recovered and separated into plant organs. The alkaloid contents in leaves and stems remained almost unchanged after ensiling, whereas a considerable reduction in alkaloids (up to 86%) was observed in the flower heads. Inflorescences generally contain high alkaloid concentrations and their reduction was mainly due to decomposition of the capitules, which might have been spread in the silage, contaminating it further. Taken together, both colchicine and pyrrolizidine alkaloids were not significantly reduced during ensiling. Because it is possible that the remainder of the alkaloids unrecovered from the toxic plants could have leached and may have contaminated the rest of the silage, we suggest that grass silages contaminated with these toxic plants should be handled with the same caution as the original roughage mass. Feedstuff containing more than 2-3% of these toxic plants should not be fed to animals.