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 various animal species, but studies in human postnatal brain tissue are lacking. Therefore, we investigated CYP19 mRNA expression in human temporal lobe tissues. We studied biopsy materials removed at neurosurgery from 34 women, 32 men and 10 children with temporal lobe epilepsy. Quantification of CYP19 mRNA was achieved by nested competitive reverse transcription-PCR. CYP19 mRNA concentrations did not differ significantly between women (2.6 +/- 0.6 arbitrary units, aU; mean +/- SEM) and men (1.6 +/- 0.3 aU) nor between cerebral cortex tissue (2.0 +/- 0.4 aU) and subcortical white matter tissue of adults (2.4 +/- 0.7 aU), but they were significantly lower in cerebral cortex specimens of children (0.9 +/- 0.6 aU) than in those of adults (p < 0.02). In conclusion, CYP19 mRNA is expressed in the temporal lobe of children and adults. CYP19 mRNA concentrations are significantly lower in specimens of children than in those of adults.