The nucleotide sequence of the T24 human bladder carcinoma oncogene was determined, and the coding and noncoding sequences of the genome were identified. The amino acid sequence of p21, the translational product of the T24 oncogene, was predicted from the nucleotide sequence of the oncogene. Comparison of this sequence with that of the normal cellular homolog showed that a single point mutation in the coding sequences of the T24 oncogene resulted in the acquisition of transforming properties. Other differences between the T24 oncogene and its normal cellular homolog were found in the 5' noncoding and 3' noncoding sequences, but these differences appear to be due to polymorphism and do not play a significant role in the transformation process.