Subacute oxalic acid poisoning was reproduced by the administration of varying doses of oxalic acid. The amount needed varied according to the nutritional status of the animal immediately prior to the experimental period. If lucerne was present in the diet or if calcium or strontium was added much larger doses were tolerated. Such an animal excreted large amounts of oxalic acid as oxalate in the faeces, and as carbonate and oxalate in the urine. In animals which failed to survive the blood urea rose, while the amount of carbonate in the urine did not. In many such animals there was a decrease in blood calcium. It is considered that the major portion of the oxalate is decomposed by bacterial action in the rumen and that the primary factor in subacute oxalic acid poisoning in sheep is rumen dysfunction due to its effect on the pH of the rumen.