Estrogens are synthesized from C19 steroids by a unique form of cytochrome P450 aromatase. Expression of the human CYP19 gene involves tissue specific use of alternative promoters. In the present study, an RT-PCR procedure was used to amplify and quantify various transcripts expressed in human granulosa cells. Cells were aspirated together with follicular fluid from Periovulatory ovarian follicles present in ovaries of 14 patients undergoing a treatment for in vitro fertilization. Sequencing of PCR products demonstrated the presence of exon I.4-specific transcripts in addition to exon P.II, exon I.3 and I.3-truncate transcripts. Quantitative results confirmed that exon P.II specific transcripts were largely predominant compared to other exon-specific transcripts, and that exon I.4-specific transcripts were the least abundant.