Fibronectin can be detected in the plasma and the extracellular matrix of the uterus of pregnant women. Studies so far have compared individual observations, whilst serial investigations during pregnancy, and during and after parturition have not been carried out. Plasma fibronectin levels were measured in 153 women with healthy pregnancies in relation to the gestational age. During parturition, blood was taken from the inception of labor through to parturition, and on the 1st, 3rd, and 5th days after parturition. The investigations of the plasma fibronectin level in pregnant women show constant concentrations up to the 35th week of pregnancy. From the 36th week onward the fibronectin rises significantly before dropping to the initial values at the start of labor. The elevated fibronectin concentration in the last 4 weeks before delivery could be explained both by renewed, elevated synthesis in the uterus and placenta as well as by lower consumption. The decline in the fibronectin level with the onset of labor could be caused by an elevated enzymatic induction in the uteroplacental unit in connection with the start of parturition.