The capacity of a primitive human retinoblastoma cell line (Y-79) to differentiate into several cell types of normal human retina was investigated. Cells were studied in suspension and monolayer cultures, in serum-free or serum-supplemented medium, and in the presence or absence of differentiating agents such as N6O12-dibutyryl adenosine 3',5'-cyclic monophosphate (dbc-AMP) and sodium butyrate (Nabut). Electron microscopy, immunohistochemistry for detection of myelin basic protein (MBP), and formaldehyde-induced fluorescence (FIF) for catecholamines were performed. Treated cells exhibited morphologic characteristics supportive of differentiation toward photoreceptors, conventional neurons and glial cells, increased FIF reactivity, and MBP expression. Growth in serum-free medium without differentiating agents led to a similar but less enhanced morphologic differentiation. These results confirm the concept that human retinoblastoma originates from a primitive neuroectodermal multipotential cell.