A thin layer chromatography experiment of medical importance is described. The experiment involves extraction of lipids from simulated amniotic fluid samples followed by separation, detection, and scanning of the lecithin and sphingomyelin bands on TLC plates. The lecithin-to-sphingomyelin ratio is calculated. The clinical significance of this number is discussed. Since this is a procedure that is often performed in medical laboratories, most of the supplies and materials for the experiment are commercially available in kit form.