Diseases and losses were registered in dependence on vitamin A supply with 2,035 pigs (6.5-114 kg live weight). The histologic examinations comprised various organs of 72 animals. The content of the main protein fractions as well as antibody titre after supplementing antigenes were determined in the serum of 104 animals. The feeding of a vitamin-A- and carotinefree casein-starch-respectively a Vitamin-A-free cereal-soybeanmeal-diet led to deficiency symptoms after 7-8 respectively 16-19 weeks of experiment particularly in the shape of nervous disturbances and voice affectations. Histologically a hyperplasia and a metaplasia of the epithelium of the big ducts in the salivory gland could be proved. The repletion of a part of the avitaminotic animals by means of oral (500 I.U./kg feed) and parenteral (500,000 to 1,000,000 I.U. i.m.) vitamin A administration is proof of a lack of vitamin A. Vitamin A and provitamin dosage did not influence diseases and losses with the exception of the occurrence of deficiency symptoms. The protein content of the serum as well as that of the globulin fractions alpha, beta, gamma did not change, the albumin content was lower in the groups without vitamin A (p greater than 0.05). Antibody titre against the lipopolysaccharide of salmonella dublin and human gamma globulin were diminished in piglets and fattening pigs fed vitamin A free (p less than 0.05). Taking the criterion of animal health, a vitamin A requirement higher than for growth (250 I.U./kg feed) cannot be derived.