Prostaglandin (PG)E and F equivalents have been determined in fallopian tubes from 26 women by radioimmunoassays following appropriate extraction and separation procedures. Both PGE and F equivalents at ranges between 5 and 100 ng/g wet weight exhibit profiles of increasing concentrations along the oviduct with low contents at the uterotubal junction and maximal levels in the fimbrial region. During the luteal phase of the cycle about 2-fold higher levels of PGE and F equivalents were detected than during the follicular phase in both the ampullary and isthmic portion of the oviduct. A general decline of PG levels was observed in tissues from patients at the perimenopause. The distribution of PGs within the oviduct is compatible with a preferential localization in its mucosal part, which may represent the main target for a progesterone-mediated stimulation of PG production during the luteal phase.