A dairy milking approximately 100 cows had five heifers and three dry cows show signs of bloat, ataxia, recumbency, and death within a 3-day period. All died within 48 hours of onset of signs and many succumbed in 24 hours or less, despite bloat treatment and fluid therapy. Extensive diagnostic testing, including necropsies, bacteriological testing, and blood work, did not reveal a diagnosis. A farm investigation was conducted to find risk factors associated with the loss of cattle. Ocular fluid obtained after an isolated heifer death two months later revealed a markedly elevated ammonia concentration and led to the diagnosis of urea toxicosis. This paper will discuss the case history, diagnostic testing, differential diagnoses, a farm investigation, urea metabolism, urea toxicosis, urea feeding recommendations, ocular fluid sampling, treatment and prognosis for urea toxicosis, and the farm outcome.