Direct-contact toxicity tests were conducted to determine the susceptibility of adults of susceptible (S) and aldrin-resistant (R) strains of seedcorn maggot, Hylemya platura (Meigen), onion maggot, H. anliqua (Meigen), and cabbage maggot, H. brassicae (Bouché) to technical chlordane. Comparison of LD50 values obtained with Sand R strains of the root maggots indicated that the resistance levels to aldrin for the 3 species ×504, 1213, and 947, respectively. The aldrin-resistant strains were resistant also to chlordane, with resistance levels at the LD50 being ×119, 238, and 90, respectively. The sample of reference-grade chlordane used contained 8.46% heptachlor, suggesting that a significant proportion of the resistance shown to technical chlordane was due to the presence of heptachlor in the sample.