The conversion of androgens to estrogens by CYP19 (cytochrome P450AROM, aromatase) is an important step in the mechanism of androgen action in the brain. CYP19 expression has been demonstrated in the brain of various animal species and in the human temporal lobe. Studies on postnatal CYP19 expression in various other areas of the human brain are rare and carried out in a limited number of post mortem obtained tissue. Therefore, we investigated CYP19 mRNA expression in fresh human frontal and hippocampal tissues and compared them to the expression in temporal neocortex tissues. We studied biopsy materials removed at neurosurgery from 45 women and 54 men with epilepsy. Quantification of CYP19 mRNA was achieved by nested competitive reverse transcription-PCR. CYP19 mRNA concentrations were significantly higher in temporal (2.29+/-0.40 arbitrary units, AU, mean +/- SEM; n = 57) than in frontal neocortex specimens (0.92+/-0.17 AU; n = 18; P<0.04). In hippocampal tissue specimens CYP19 expression (1.41+/-0.18 AU; n = 24) was lower than in temporal neocortex specimens, but the difference did not reach statistical significance. Sex differences were not observed in any of the brain regions under investigation. In conclusion, CYP19 mRNA is expressed in the human temporal and frontal neocortex as well as in the hippocampus. Regardless of sex, CYP19 expression was significantly higher in the temporal than in the frontal neocortex.