The selenium content of the vegetation of the Karoo has been investigated. It is clear that given suitable conditions numerous species of plants in this area can take up moderate to dangerous amounts of the element. A tentative classification of these plants on the basis of apparent selenium uptake has been attempted. Correlation between selenium content of the vegetation and the incidence of geeldikkop and enzootic icterus is demonstrated. The effects of veld mismanagement in relation to these disease problems are indicated.