One-micron plastic "thick" sections, usually stained with toluidine blue, are indispensable light microscopic adjuvants for the selection and evaluation of tissue blocks prior to electron microscopy. Plastic thick sections may also be the only practical alternative to routine histologic sections when tissue specimens are limited or too small for processing in paraffin. In all cases, however, plastic sections provide superior light microscopic resolution compared to paraffin sections, but lack the compatibility with the wide variety of special stains that make paraffin sections so versatile.