In a screening of South African indigenous food plants for antioxidant activity by testing for inhibition of lipid peroxidation, the "potherbs" Amaranthus sp., Sisymbrium thellungii, and Urtica dioica had very high activity. This activity was greatest in the boiled extract of Amaranthus sp. and the boilet and aqueous extracts of Sisymbrium thellungii and Urtica dioica. The activity in the aqueous extract of Nasturtium aquatica was lost by boiling. High activity was also obtained with the teas Galium aparine and Aspalathus linearis (Rooibos) and with the tuber Colocasia esculenta.