The dose-response relationship for hepatic 7-ethoxyresorufin-O-deethylase (EROD) induction in barramundi (Lates calcarifer) was examined under controlled laboratory conditions for 15 d using farm-reared barramundi. These results were compared with EROD activity measured in barramundi collected from two rivers catchments (impacted and nonimpacted) in northern Queensland, Australia. Barramundi were dosed by intraperitoneal injection with a known cytochrome P4501A (CYP1A) inducer, beta-naphthoflavone (beta-NF), at 5, 10, and 50 mg kg(-1) using two controls: A vehicle control (corn-oil injected) and an experimental control (no injection). The EROD induction occurred within 4 h in the 5, 10, and 50 mg beta-NF kg(-1) exposures, reaching mean maximum activities of 88.6 (+/-51.9), 85.5 (+/-91.7), and 149.1 (+/-106.4) pmol min(-1) mg protein(-1), respectively. Mean EROD activities remained low in the corn-oil controls (2.1+/-1.8 pmol min(-1) mg protein(-1)) and experimental controls (5.3+/-4.4 pmol min(-1) mg protein(-1)) throughout the study. Barramundi demonstrated a rapid response curve, which was dose dependent (50 > 10 > 5 mg beta-NF kg(-1)) and decreased progressively over time from induction. Measurement of total cytochrome P450 content (nmol mg protein(-1)) was not dose dependent. The EROD activities from field-collected barramundi from the Johnstone River (impacted) and Olive River (nonimpacted) suggest exposure to low-level contaminants in the Johnstone River fish only. With more controlled laboratory and field studies, barramundi have the potential to become a major indicator species in assessing exposure to environmental contaminants in coastal areas throughout northern Queensland, Australia.