Inactivation of the tumor suppressor gene RB1 is causal for development of retinoblastoma, a tumor of the neural retina arising in children under the age of five. In addition, secondary RB1 mutations are found in many other tumor types. To investigate retinoblastoma formation in vitro, stem cells with inactivated RB1 can be differentiated into neural retina. To enable such studies, two sublines of hESC line H9 carrying mutations in RB1 exon 3 in heterozygous or homozygous state were generated and characterized. Homozygous mutation led to loss of RB1 protein expression.