The epidermal remains of 4 poisonous plant species that produce acute intoxication in ruminants were quantified by microhistological analysis in the gastro-intestinal content of sheep experimentally poisoned. These species were 'romerillo' or 'mio mio' (Boccharis coridifolia DC); 'duraznillo negro' (Cestrum parqui L'Hbrit.); 'poison hemlock' (Conium maculutum L.), and 'sunchillo' (Wedeliu glaucu (Ott.) Hoff.). All of these species produce important economic losses of livestock in the Flooding Pampa, Buenos Aires, Argentina.The plants used for intoxication were at the vegetative stage of growth. Results indicate that the microhistological technique can he used to confirm the diagnosis of ruminant intoxication by duraznillo negro, romerillo, and sunchillo, but not by poison hemlock because digestion degrades its fragments beyond recognition.It would be convenient to sample the final sections of the digestive tract to confirm romerillo and sunchillo ingestion, because their fragments tend to concentrate there. The uniformity of duraznillo negro fragment distribution would allow identification of this species from any section of the digestive tract. However, the considerable variability in fragment distribution found among animals poisoned with the same plant species makes it necessary to sample more than 1 digestive region if only 1 animal is available for necropsy.

Romerillo' (Baccharis coridifolia DC), 'duraznillo negro' (Cestrum parqui L'Herit.), and `sunchillo' (Wedelia glauca (Ort.) Hoff.) are highly toxic species producing important economic losses of livestock in Argentina. This study assessed the accuracy and precision in the estimation of the percentage and the mass of these species in the ingesta and feces of sheep experimentally poisoned. This study also evaluated whether the quantified percentage and the calculated mass of each toxic species in the rumen+reticulum, the easiest region to sample, are good estimates of their relative consumption. Results indicate that if

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