Accumulating evidence provides support for the idea that determination of UGT1A1 polymorphisms before irinotecan (CPT-11) treatment is clinically useful and important for predicting and avoiding related toxicities. In 2005, the irinotecan label was updated in the USA in order to provide pharmacogenetic information. A dose reduction of irinotecan should be considered for patients known to be homozygous for the UGT1A1*28 allele when administered in combination with other agents or as a single agent. The feasibility of genotyping for DNA polymorphisms prior to treatment depends on the availability of rapid, accurate and efficient genotyping methods. Genotyping of UGT1A1*28, *6 and *27 by the newly developed Invader UGT1A1 Molecular Assay agreed completely with the genotyping results obtained with established methods, and this molecular assay provides rapid detection of polymorphisms. This newly developed method for detecting UGT1A1 polymorphisms is feasible and has the potential to be widely used for rapid and accurate screening before irinotecan treatment.