The NF1 gene has been isolated and partially characterized. The discovery that NF1 functions as a ras GTPase activator protein has led to new opportunities for understanding the pathology of this disease. The approximately 11 kilobase (kb) NF1 consensus cDNA sequence contains an open reading frame encoding a peptide of 2818 amino acids. DNA blot and polymerase chain reaction analysis indicate that the NF1 gene consists of over 50 exons spanning 300 kb of chromosome 17.