Laboratory studies were conducted to determine some of the insecticidal properties of AC303,630, the lead candidate of a newclass of compounds known as pyrroles, against larvae of Heliothis virescens (Fabricius). Topical and gavage applications to fifth instar H. virescens demonstrated that AC303,630 possessed both cuticular-contact and stomach insecticidal activity. However, AC303,630 was significantly more toxic to larvae via ingestion than by contact. Residue-on-glass and leaf-dip assays demonstrated contact and stomach toxicity of AC303,630 against larvae relative to that of standard pyrethroid, carbamate, organophosphate and cyclodiene insecticides. In comparing LC(50) values between first and third instar H. virescens (leaf-dip assays), it was found that agerelated tolerance by larvae to AC303,630 occurred at a slower rate than that of tolerance to selected standard insecticides. Results from laboratory trials also indicated no occurrence of multiple resistance to ACS03,630 by pyrethroid-resistant H. virescens. Results from these studies suggest that AC303,630 has potential to be a very effective insecticide against Heliothis/Helicoverpa in cotton.