The in vitro conversion of [14C]arachidonic acid by endocervical mucosa and cervical tissue specimens obtained in first trimester (9-12 w) and term pregnant patients (37-39 w) was studied in whole-cell homogenates. All radiolabelled products of the arachidonic acid cascade were extracted, purified and separated utilizing silicic acid chromatography, thin-layer chromatography and reversed phase partition chromatography and identified with radio-gas chromatography and gas chromatography-mass spectometry. Both types of tissue produced PGF2 alpha and PGE2, as well as TxB2. In cervical tissue specimens there was a significant increase in the production of all these three prostaglandins as the pregnancy progressed, whereas no such difference was seen in homogenates of endocervical mucosa. In both endocervical mucosa and cervical tissue specimens there was a highly significant increase in the production of a so-far unknown compound(s), in samples from term patients as compared with samples from first-trimester patients. The possible participation of this metabolite of [14C]arachidonic acid in the regulation of cervical ripening is discussed.