Novel single nucleotide polymorphisms in the human UDP glycosyltransferase 1 (UGT1A1) gene are described. In addition, various genotypes, haplotypes and haplotype pairs for the UGT1A1 gene that exist in the population are described. Compositions and methods for haplotyping and/or genotyping the UGT1A1 gene in an individual are also disclosed. Polynucleotides containing one or more of the UGT1A1 polymorphisms disclosed herein are also described.
