The influence of aflatoxins B1, B2, G1, and G2was studied on the electron transport chain (from water to methyl viologen) of freshly lysed chloroplasts from maize(Zea maysL.) and peas(Pisum sativumL.). A partially purified extract containing all four toxins was added to a chloroplast suspension. Basal, phosphorylating, and uncoupled electron transport were assessed immediately after its addition and 4 min later. In maize chloroplasts, all three types of electron transport were inhibited by the mixture. The inhibition did not increase with time. The basal electron transport of pea chloroplasts was inhibited very slightly (20%) by the aflatoxin mixture. Commercially purified aflatoxins B1, B2, G1, and G2were tested individually. Only aflatoxins B1and B2showed effects on the chloroplasts of both species. With 16 μ?/ml of aflatoxin B2in the assay medium, the three kinds of electron transport were drastically inhibited both in maize (75%) and pea (60%) chloroplasts. Aflatoxin B1showed no effect on maize chloroplasts; however, a slight increase (31 %) was observed on the electron transport rate of pea chloroplasts. Differential response between electron transport rate in maize and pea could be related to the toxin's chemical structure, with a slight difference between molecules resulting in enormous differences in activity.