Summary.-Four human and 4 rat astrocytomata and mammalian adult brain and spinal cord were examined by indirect immunofluorescence with human serum containing smooth muscle antibody. Cryostat sections of astrocytomata showed staining of the tumour cell cytoplasm and processes while in normal adult brain and spinal cord the entire astrocyte stained. Impression film and tissue culture monolayers of astrocytomata showed staining of cell processes and a fine, filamentous network in the cell body. The reaction with astrocytoma tumour cells was stronger than that with the corresponding normal astrocytes. Specificity of the staining reaction was established by its prevention on neutralization absorptions of the serum with -extracts or homogeneous of smooth muscle. The presence of smooth muscle-associated antigen in astrocytes and astrocytomata is indicative of contractile protein providing a mechanism of cell movement in vivo.

Summary. Tissue culture iiionola\crs of scvfii hiniian intracraiiia! himours compri.sinH 2. a.sti()cytonias, 3 meniiigioinas, 1 secondary squaniims cell carcinoma and 1 secondary adenocarcinoma were examined by a double immunofluorescent .•jtaininj; techniqiit' to demoRStrate Concanavalin A (Con A) surface receptors and cytoplasmic actin in the same cell. Tumour cells, treated with fiuoresceinisothiocyauate-labellwl Cini A (FITC-Con A) showed .staininii in cell marniu.'; or in a raiidoin distribution over the cell surface. lnciiliatinK the cells with FITC-Con A at .37° for increasing periods of time resulted tir.st in staining of clusters and later of perinuclear globules. CIclls, prctreated with 4% paraformaldehyde at 4° for 10 min or with cytoclialusin B ut .37° for .30 min showed staining restricted to cell margins. In the cytochala.sin B-treated cells, the peripheral staining was in the form of coarse clusters. Double fluorochrome studies .showed that the anti-actin antibody (AAA) staining occurred in sites closely related to those stained l)y FITC-Con A both in untreated as welt as in cytiiclialusin B-tveated cells. The findings suggest that Con A receptors, as an example of a stable cell membrane determinant in human tumour cells, are as.soeiated with actin and that their m()l)ilit>-on the cell surface is dependent on an intact cytopiasmic actin system.