Kinetics of lead citrate staining of thin sections for electron microscopy

The staining of thin sections with lead citrate shows an initial increase followed by a decrease much later; the rate of the initial increase and subsequent loss varies for different cellular components. The decrease eventually reaches a stable minimum. At this level electron scattering is less than that of unstained sections, demonstrating a loss of biological material. Lead citrate used as a poststain following uranyl acetate causes an increase in electron density that is independent of staining time over 1-30 min; this increase appears to depend only on the quantity of uranyl acetate already bound, implying that the lead binds predominantly to the uranyl acetate.