Cells showing CPE and containing novel bunyavirus RNA were collected for thin-section electron microscopy. After discarding the culture supernatant, virus-infected cells (50 mL) were mixed 1:1 with 4% glutaraldehyde (paraformaldehyde), placed onto Formvar-carbon-coated grids, and stained with 1% methylamine tungstate. Specimens for thin-section electron microscopy were prepared by dehydrating washed cell pellets with serial dilutions of acetone and embedding in epoxy resin. Ultrathin sections were cut on an Ultracut LKBV ultramicrotome, stained with uranyl acetate and lead citrate, and examined under a transmission electron microscope (JEM-1400).