A competitive polymerase chain reaction (PCR) method was used to determine the Ah-receptor mRNA content in several tissues of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-sensitive C57BL/6J and less susceptible DBA/2J mice. Total RNA from liver, lung, thymus, spleen, heart, kidney, brain, muscle, and placenta was isolated and reverse-transcribed. Each cDNA was coamplified with a known amount of homologous competitor fragment, and PCR products were quantified by extrapolating against a standard curve. The Ah-receptor mRNA was expressed in all tissues examined. The highest mRNA level was found in lung, yielding concentrations of 31.7 +/- 11.0 X 10(3) molecules/100 ng RNA and 20.3 +/- 8.9 X 10(3) molecules/100 ng RNA in C57BL/6J and DBA/2J mice, respectively. In heart, liver, thymus, brain, and placenta the Ah-receptor mRNA content was about 5-10 times lower than in lung. Low levels were found in spleen, kidney, and muscle. Statistical analysis of the data revealed no significant differences regarding the Ah-receptor mRNA expression between C57BL/6J and DBA/2J mice. From these results it is suggested that factors other than differences in Ah-receptor mRNA content may be responsible for different susceptibility of C57BL/6J and DBA/2J mice toward TCDD.