Blesbuck (Damaliscus dorcas phillipsi) and springbuck (Antidorcas marsupialis) were found to be more susceptible to dieldrin and its photoisomer than any vertebrates reported on previously in the literature. In blesbuck the mean cumulative lethal dose of dieldrin at various dietary levels was 9,07 mg/kg and of photodieldrin 1,90 mg/kg. Under field conditions the calculated median lethal dose of photodieldrin to blesbuck was 1,21 mg/kg; to springbuck it was 3,97 mg/kg. In both species rams were more susceptible to photodieldrin than ewes. It was proved that antelope mortalities on veld sprayed with dieldrin for harvester termite (Hodotermes mossambicus) control was principally due to photodieldrin intoxication. In addition to the usual violent nervous signs encountered in chlorinated hydrocarbon intoxication a dumb syndrome, in which blindness was rather characteristic, was seen, especially in the field cases. The pathological changes in the blesbuck and springbuck were similar. Degenerative lesions typical of various conditions, including chlorinated hydrocarbon poisoning, were encountered in the skeletal muscles, myocardium, kidneys and liver of cases of both dieldrin and photodieldrin poisoning. The severity and widespread nature of the lesions in the skeletal muscles and myocardium of natural cases were reminiscent of white muscle disease and capture myopathy. Congestion, oedema and glial swelling of the brain were constant features.