Three morphologically and immunohistochemically distinct types of cell were present in primary cultures of adult rat olfactory nerve and glomerular layers of the olfactory bulb. One cell type was multipolar and stained positively for glial fibrillary acidic protein; a second type had fried egg-like morphology and stained with antibodies to epitope ED1; the third cell type had fusiform morphology, reacted with antibodies to vimentin and laminin and was glial fibrillary acidic protein- and ED1-negative. Trypsinization of these primary cultures (3 min, 37 degrees C), detached multipolar and fusiform cells only. When detached cells were set up in secondary culture on a glass substrate, fusiform cells did not attach, resulting in a pure culture of multipolar cells. Multipolar cells were glial fibrillary acidic protein- and myelin basic protein-positive and had the properties of so-called ensheathing cells or Blanes' glia. Immunoreactivity with anti-nerve growth factor receptor and anti-fibronectin allowed us to identify four distinct populations of multipolar ensheathing cells. One population was nerve growth factor receptor-positive, fibronectin-negative. A second was nerve growth factor receptor-negative and fibronectin-positive. A third was positive for both markers and the remaining cells did not stain for either of them. The morphological and immunological characteristics of cultured cells from olfactory nerve and glomerular layers were similar to those of Schwann cells and the similarities could account for the permissivity to axonal growth of the olfactory bulb.