Given the absence of data on the frequencies of GSTM1 and GSTT1 genotypes in our population, we decided to carry out this case-control study with the aim to establish firstly their frequencies in the population and secondly estimate the possible link between the null genotypes and the occurrence of chronic myeloid leukemia in a sample of the Moroccan population. This evidence concerns the gene GSTM1 and chronic myelogenous leukemia, BCR-ABL1 positive.