A small dermatan sulphate proteoglycan has been isolated from the human uterine cervix. The concentration of this proteoglycan has been shown to decrease during pregnancy. To study the mechanism behind this change fibroblasts from the human uterine cervix were established in culture. Their synthesis and secretion of proteoglycans were investigated by incubating the monolayer with 35SO4 and (3H) leucine for 48 h. Two dermatan sulphate proteoglycans and one heparan sulphate proteoglycan were isolated from the medium. The cell layer contained the same proteoglycans although in different proportions. The major dermatan sulphate proteoglycan accounting for 55% of the total macromolecular 35S was small with a molecular weight (MW) of 100,000 daltons. The side chains were calculated to be approximately 1-3 per protein core and included more than 50% iduronic acid containing disaccharides. This small dermatan sulphate proteoglycan is very similar to that isolated from the intact human uterine cervix. However, when cells were established in culture an additional larger dermatan sulphate proteoglycan with an MW of 400,000 daltons was synthesized. This proteoglycan was substituted for 4-8 polysaccharide side chains rich in glucuronic acid. 24% of the total macromolecular 35S were found in this proteoglycan.