Two continuous retinoblastoma cell lines were observed by scanning electron microscopy. Both cell lines spontaneously grow as a suspension of round cells in clusters, chains, and unique ring (rosette) formations. Scanning electron microscopy of suspension cells reveals some variation in the number and frequency of surface adornments such as blebs, lamellipodia, and microvilli. Although the cell lines are nonadherent to substratum and therefore assume a spherical form, highly villous cells are not characteristic of the entire cell populations. When WERI-Rb1 and Y79 are seeded onto a polyornithine-treated substrate, attachment and growth as adherent cultures are evident. With selective attachment on a positively charged substrate, we observe alteration of membrane architecture with the extension of cytoplasm and filopidia. In addition, WERI-Rb1 cell-to-substratum adhesion induces morphological changes suggestive of neuronal cell differentiation.