High-voltage transmission electron microscopy and cryo-ultramicrotomy together with scanning electron microscopy and some conventional transmission electron microscopy of ultrathin sections have been applied to the mucous surfaces of bovine olfactory and respiratory epithelia. Distal segments of olfactory cilia tend to run in parallel and could be followed over distances up to about 30 micrometer using high-voltage electron microscopy. This technique and scanning electron microscopy showed that on average 12--13 of such cilia could be observed per nerve ending. After correction for obscured cilia this number becomes about 17. High-voltage micrographs and micrographs made from sections prepared with a cryo-ultramicrotome showed the presence of electron-lucent pockets inside the olfactory mucus. The latter technique also showed that the mucus itself is not fibrous, but rather a continuum varying in electron density. The mucus layer contains various granular structures. Ciliary and microvillar membranes appear thicker with cryo-ultramicrotomy than when the sections are prepared with conventional techniques. The cores of the axonemal microtubules in olfactory as well as in respiratory cilia are darkly stained with this technique. Vesicles present inside the nerve endings are also darkly stained. Dimensions and some other numerical values of interest in olfaction are presented.