The 7-ethoxyresorufin O-deethylase (EROD)- and aryl hydrocarbon hydroxylase (AHH)-inducing potencies and lethalities of a technical preparation of polychlorinated naphthalenes (PCNs) (Halowax 1014, approximate congener ratio: 20% tetrachloronaphthalenes, 40% pentachloronaphthalenes, 40% hexachloronaphthalenes), a mixture of 50% 1,2,3,5,6,7-hexachloronaphthalene and 50% 1,2,3,4,6,7-hexachloronaphthalene (HxCN-mix), and 1,2,3,4,5,6,7-heptachloronaphthalene (HpCN) were studied in chicken (Gallus domesticus) and eider duck (Somateria mollissima) embryos. Mortality and hepatic EROD activity were determined on day 10 of incubation in chicken embryos exposed to various doses of the PCNs via the air-sacs of the eggs on day 7. The HxCN-mix and Halowax 1014 proved to have both embryolethal and EROD-inducing properties, while the HpCN had low EROD-inducing potency and embryolethality. ED50 values for EROD induction by the HxCN-mix and Halowax 1014 were estimated to be 0.06 mg/kg egg and 0.2 mg/kg egg, respectively. Fifty percent of the chicken embryos died (6/12) when given 3.0 mg/kg of the HxCN-mix while a similar dose of Halowax 1014 caused mortality in 4 out of 12 chicken embryos. The dose-response curve for EROD induction by Halowax 1014 exhibited a decline after the maximal level was reached. When Halowax 1014 (1.0 mg/kg egg) was coinjected with 3,3',4,4',5-pentachlorobiphenyl (PCB IUPAC #126) (0.1 microgram/kg egg) no additive effects on EROD activity were found, but when the same dose of Halowax 1014 was coinjected with a dose of PCB #126, known to cause maximal induction (1.0 microgram/kg egg), the resulting EROD activity was lower than that caused solely by 1.0 micrograms PCB #126/kg egg.(ABSTRACT TRUNCATED AT 250 WORDS)