Cuticular and gastrointestinal penetration, in vivo metabolism, and excretion of [14C]acridine were investigated in the nymphal cricket Acheta domesticus (L.) to find a pharmacodynamic basis for this insect's differential susceptibility to acridine at different life stages. Topically applied [14C]acridine readily penetrated the cuticular exoskeleton of nymphs (half‐time of penetration, 48 min). Radiolabeled compounds appeared in the hemolymph within 0.5 h after ingestion of [14C]acridine and continued to move across the gut wall for 7.5 h. The biological half‐time was 18 h and the rate constant for elimination was 0.039 h−1after ingestion. Within 5 d after dosing, 97% of the dose was excreted. Several metabolites were present in the feces of nymphs fed [14C]acridine, and less than 13% of the extractable radioactivity was parent compound. The cuticle and the gastrointestinal tract proved to be ineffective barriers to acridine entry in A. domesticus. However, the ability to readily metabolize and excrete acridine probably contributes to the higher acridine tolerance observed in the nymphs and adults than in the eggs, which are susceptible to toxic effects.