Three of the most commonly used bioassay methods for monitoring insecticide resistance in Lepidoptera are the adult vial test, the topical application test and IRAC method No.7. Each method has its advantages and disadvantages, as discussed in this paper, and the best choice depends largely on the objectives of any particular study and the skills and facilities available. All three methods have proven successful in large-scale monitoring programmes in various countries, but IRAC No.7 does have distinct benefits i) where facilities and equipment are limited, ii) when a range of stomach and contact acting insecticide groups are being tested, and iii) when it is necessary or convenient to use readily available formulated products.