In order to study the influence of temperature on vitellogenin gene and estrogen receptor gene expression in primary hepatocytes from rainbow trout (Oncorhynchus mykiss), cells were exposed to 17beta-estradiol, bisphenol-A and nonylphenol for 48 and 96 hr. Induction of vitellogenin-mRNA expression was detected in a non-radioactive dot blot/RNAse protection assay and by RT-PCR. In the dot blot/RNAse protection assay, the estrogenic potentials of bisphenol-A and nonylphenol were about 10(4)- to 10(5)-fold and 10(5)-fold lower than that of 17beta-estradiol, respectively. The relative estrogenic potential did not show any difference between 14 and 18 degrees C. In contrast, at 18 degrees C, RT-PCR analysis revealed increased amounts of vitellogenin- and estrogen receptor-mRNA after 12 and 24 hr of exposure to 17beta-estradiol, if compared to 14 degrees C. Owing to increased vitellogenin gene expression at 18 degrees C, the sensitivity of primary hepatocytes to 17beta-estradiol and bisphenol-A could be increased.