A new continuous retinoblastoma cell line (Rb 355-7) derived from a nonfamilial unilaterally-affected child was studied morphologically and with regard to HLA expression. The tumor was compared with two older and widely studied cell lines, the Y-79 and WERI-Rb1 strains. The Rb 355-7 line grew in tissue culture in clusters and chains. Its doubling time was calculated to be 4.4 days. In contrast to the Y-79 and WERI-Rb1 cell lines, the Rb 355-7 showed a paucity of HLA expression.