A simple, rapid multiplex PCR-RFLP method will help in routine simultaneous identification of SNPs and determination of allelic and genotypic frequencies of CYP3A4*4, CYP3A4*18B and CYP3A4*22 which can be applied in various pharmacogenetics studies to predict patients’ responses to treatment and serve as a basis for personalised treatment of breast cancer as well as in many other diseases. The gene discussed is CYP3A4; the disease is breast cancer.