It is used as a negative stain in electron microscopy. In fact, most procedures in electron microscopy for biology require the use of uranyl acetate. 1% and 2% uranyl acetate solutions are used as an indicator, and a titrant in stronger concentrations in analytical chemistry, as it forms an insoluble salt with sodium (the vast majority of sodium salts are water-soluble). Uranyl acetate solutions show evidence of being sensitive to light, especially UV and will precipitate if exposed.
Commercial preparations of uranyl acetate are made from depleted uranium and have a typical radioactivity of 0.37 - 0.51 µCi/g. This mild radioactivity level is not sufficient to be harmful while the material remains external to the body. However it is very toxic by ingestion and if inhaled as dust or by skin contact if skin is cut or abraded and there is a danger of cumulative effects from long term exposure.