Datura poisoning of horses is extensively reviewed. An outbreak of intractable impaction colic affecting 18 of 83 horses was stopped by withdrawing dried tef hay contaminated with young Datura plants. The dried, botanically identified Datura stramonium and D. ferox contained respectively 0.15% mass/mass (m/m) hyoscyamine as well as 0.16% m/m hyoscine (scopolamine) and only hyoscine at a concentration of 0.11% m/m. Immature, unidentifiable plants resembling D. stramonium, contained 0.14% m/m and 0.12% m/m of the 2 respective tropane alkaloids. The outbreak was characterised by protracted and repeated colic attacks due to impaction of the large colon and/or caecum without any other anti-muscarinic signs. Comparative analyses of single specimens of dried seed of the 2 species collected from both fertilised and waste areas revealed that young South African Datura spp. had levels of tropane alkaloids comparable to those in the well-known toxic seed and were, consequently, equally toxic. The inherent danger of tef hay being contaminated with Datura is emphasised. To our knowledge this is the 1st field case of poisoning in horses ascribed to the vegetative parts of Datura spp.