4-methylimidazole (4-MI) was given orally to a cow in increased dosages to determine if it could be detected in her milk and be present at a concentration high enough to affect her nursing calf. 4-MI was found in the milk, but the calf remained clinically normal throughout the experiment. The cow died after the fourth dose of 20 g 4-MI. Four groups of 10 mice each were given oral doses of water, normal milk, cow's milk after low doses of 4-MI, or cow's milk after high doses of 4-MI. All mice remained healthy after a 2-week feeding trial. Six 3-day-old calves were given 4-MI directly in their bottles of milk up to 2 times the highest level found in toxic feed with only mild depression noted in one calf. Two pregnant cows were given 4-MI pre-partum to determine if it would get into the colostrum at higher levels. Both cows received 4-MI 3 days before they calved and for 2 weeks afterward. Cow A exhibited trembling, excessive salivation and incoordination after the initial dose. Cow B and the newborn calves were never affected throughout the experiment. Each time the dose of 4-MI reached 1.5 g or more, Cow A would exhibit the previously described signs. 4-MI was detected in the colostrum but not in higher concentrations than in the other milk samples.