The neural crest gives rise to a variety of tissues, including peripheral neurons, Schwann cells, melanocytes and ectomes‐enchymal cells, which include the smooth‐muscle cells of large arteries. Cell lines derived from neuroblastoma (a neural‐crest tumor) exhibit at least 2 distinct morphological cell types, a neuroblastic phenotype (N‐type) and an epithelial‐like phenotype (S‐type) with characteristics of substrate‐adhesiveness. We have analyzed 17 human neuroblastoma cell lines using a panel of monoclonal antibodies (MAbs) against cytoskeletal proteins. Three neuroblastoma cell lines (KP‐N‐SI, KP‐N‐YN and SMS‐KCN) bound an α‐smooth‐muscle actin antibody. In addition, one of these lines (KP‐N‐SI) bound anti‐desmin MAbs as determined by indirect immunofluorescence. A total of 8 cioned cell lines were obtained from the above parent cell lines. These were composed of either N‐or 5‐type cells and were confirmed to have the same neuroblastoma origin as each parent cell line by chromosomal analysis. Alpha‐smooth‐muscle actin and desmin were demonstrated In the 5‐type cloned cells by indirect immunofluorescence, as well as by 2‐dimensional Western blot analysis. These results were confirmed by Northern blot analysis using a specific probe (pSHαSMA‐3′UT) to human α‐smooth‐muscle actin mRNA. These ascertain the presence of α‐smooth‐muscle actin and desmin in neuroblastoma cell lines. These data show that, in addition to giving rise to cells with neural, Schwann‐cell and melanocyte markers, neuroblastoma can also give rise to the cells expressing smooth‐muscle cell markers.