and the whole oligonucleotide has the sequences shown in table 2 the normal residue at 857 is guanine and the whole oligonucleotide has the sequences shown in table 2 another aim of the present invention is to provide oligonucleotide molecules complementary to any of the oligonucleotide molecules described above another aim of the present invention is to provide a diagnostic assay for determining cyp1a1 genotype of an individual which comprises isolating dna from said individual amplifying for cyp1a1 pcr fragment from said dna which includes at least one of the positions 4887 4889 or 6235 thereby obtaining an amplified fragment transferring said amplified fragments to membrane filter hybridizing said membrane with allele specific oligonucleotide corresponding to at least one of point mutation at the positions 4887 4889 or 6235 and in parallel with the corresponding wild type oligo nucleotide thereby determine the cyp1a1 genotype of said individual in a preferred embodiment of the invention controls are run parallel to the above described reaction steps another aim of the present invention is to provide a diagnostic assay for determining cyp1a1 genotype of an individual which comprises isolating dna from said person making a first and a second pcr primers wherein the first pcr primers is complementary to a region 5 u2032 to one of the point mutation sites at position 4887 4889 or 6235 and the second pcr primer is complementary to a region 3 u2032 to the same one of the point mutation sites at position 4887 4889 or 6235 amplifying the sequence in between the first and the second primers thereby obtaining an amplified fragment the whole sequence of the pcr primers is given in table 1 another aim of the present invention is to provide a diagnostic.