Insect growth regulators (IGRs) such as lufenuron, methoprene, and pyriproxyfen have been important tools in the integrated pest management of cat fleas, Ctenocephalides felis (Bouché), for the past two decades. Other IGRs have been registered for the control of termite, dipteran, and lepidopterous pests including chlorfluazuron, cyromazine, dicyclanil, and precocene I, but have been not tested against C. felis. The intrinsic activity of IGRs was determined by exposing larvae to treated larval rearing media. The LC₅₀s of chlorfluazuron, cyromazine, dicyclanil, lufenuron, and precocene I against cat fleas were 0.19, 2.66, 0.04, 0.20, and 10.97 ppm, respectively. The LC₉₅s of chlorfluazuron, cyromazine, dicyclanil, lufenuron, and precocene I were 0.78, 51.24, 0.30, 0.62, and 175.05, respectively. The regression slopes of chlorfluazuron and lufenuron were 2.65 ± 0.24 and 3.40 ± 0.45 (SEM), respectively, and considerably steeper than the other IGRs tested (1.51 to 1.74). The intrinsic activity of IGRs tested is summarized as dicyclanil > chlorfluazuron = lufenuron > cyromazine > precocene I. The responses of the laboratory UCR strain to these IGRs can serve as a baseline of susceptibility until a more susceptible cat flea strain is found. Chlorfluazuron and dicyclanil look like promising candidates against cat fleas.