The purpose of this study was to investigate the applicability of flow cytometry to human placenta and to challenge the hypothesis that no cell division takes place in the last 4-6 weeks of pregnancy. Relative DNA content in individual placental cells was measured and high-resolution DNA histograms were obtained, based upon measurements of more than 10 000 cells. The fraction of cells with S-phase DNA content was lower in cases of intra-uterine growth retardation. In contrast to the earlier concept based on measurements of total organ content of DNA, this study indicates that cell division in placenta takes place right up to parturition. Small amounts of tissue are sufficient for the analyses which may aid surveillance of both normal and risk pregnancies.