Experimental feeding, dealing with long term ingestion of small daily doses of DMNA has clearly demonstrated the cumulative toxic effect of this compound in sheep. A threshold level, somewhere between 0.10 mg and 0.15 mg DMNA/kg body weight per day, can be defined below which no toxicity even in quite long-lasting feeding can be demonstrated. Above this level toxicity changes will develop, clinically in most cases, anatomically in all, if the exposure time is long enough. If the daily intake of DMNA is over this threshold level, 21–40 mg DMNA/kg body weight, it usually causes liver disease and death in sheep. Neoplastic lesions were not produced, the experimental period, however, was below the latency period for carcinogenesis.