Substances injurious to animals may be present in the air, soil, water and plants. When these substances are taken up by animals, they may have adverse effects. Whether these effects occur will depend, among others, on the nature and amount of the substance and the period for which it is taken up. Effects may occur immediately, after some time or after a prolonged period. In view of the fact that wind force is almost invariably present and therefore that the degree of dilution of the concentrations of pollutnats on immission level is generally speaking rather low, the intake of substances trough the respiratory organs will rarely show severe clinical effects. In almost every case, injurious substances will have been ingested (contaminated food and water, unless it is tap water). Adverse effects will appear in the entire or nearly herd of cattle. The importance of an adequate anamnese and correct sampling of plants-, water- and animal-samples is stressed. Accurate cattle recording also is of paramount importance. In addition to diagnosis and cattle recording, the settlement of losses is discussed.