Contrast for transmission electron microscopy (TEM) of microphase-separated saturated hydrocarbon diblock copolymers has been obtained using ruthenium tetroxide (RuO4). This technique exploits differences in the rate of transport of the oxidizing stain in rubbery amorphous Versus semicrystalline, or glassy, microdomains. Rapid quenching from above the melting (T-m), or glass transition (T-g) temperature is shown to preserve the equilibrium melt morphology in poly(ethylene)-poly(ethyl-ethylene) (PE-PEE), poly(ethylene)poly(ethylene-propylene) (PE-PEP), and poly(vinylcyclohexane)-poly(ethyl-ethylene) (PVCH-PEE) diblock copolymers; PE melts at 108 degrees C, PVCH is glassy up to about 140 degrees C, while PEE and PEP remain rubbery down to approximately -20 degrees C and -56 degrees C, respectively. Treatment of ultrathin sections of the quenched specimens with RuO4 vapor led to well-defined TEM images, that revealed microdomain type and order. These results are consistent with SANS data taken under equilibrium conditions.