Two dimensional electrophoresis is a technique whereby protein sources are organized by molecular weight and electrical charge on a polyacrylamide gel. To detect changes that may be associated with the onset of parturition, we compared electrophoresis patterns of mononuclear cell proteins and plasma proteins before and during active labor. Mononuclear cells and plasma were obtained from 5 pregnant volunteers. It appears that A-1 apolipoprotein, identified by Western Blot analysis, is increased in mononuclear cells during active labor. Conversely, a decrease in the concentration of A-1 apolipoprotein was seen in plasma during parturition. These "normal" protein patterns can now be compared with those observed in pathologic conditions including preterm labor and may allow early detection of disease by protein abnormalities before clinical signs and symptoms develop.