The status and expression of Rb gene was detected and analyzed in 19 surgical retinoblastoma specimens using Rb cDNA 3.8 kb and 0.9 kb fragment as probe and antibodies specific for synthetic Rb peptide or expressive product of Rb gene expression plasmid. DNA from those tumors had the hemizygous deletion in 3 cases, the homozygous internal deletion in 2 cases and alterated restriction fragment involving in one copy of Rb gene in 1 case. The quantity of Rb protein demonstrated either absence of reduction in all the 16 cases examined in comparison with that in normal adult retina. It suggested that there were structural or/ and functional defects of Rb gene in retinoblastoma cells and provided evidence to support Knudson’s two hit hypothesis.