The calpain family includes proteolytic enzymes, which have a high capacity to degrade cytoskeletal and muscle fibre proteins. Thus they play an important role in the fusion of myoblasts and in cell proliferation and growth. The CAPN1 gene has been selected as a ‘candidate gene’ for meat quality in many domestic animals, including chickens. Consequently, the aim of our study was to identify new polymorphisms in the promoter region of the CAPN1 gene in broilers and to nvestigate their impact on CAPN1 transcript abundance in breast muscles. The experiment used broilers of two genetic lines, fast- and slow-growing. Five new polymorphisms in the promoter region of the CAPN1 gene were identified, all of them in linkage disequilibrium (P<0.05). However, the results obtained for their association with expression level were doubtful. Therefore, we surmise that the newly discovered polymorphisms, although they alter the potential sequence binding of transcription factors, probably have just a weak effect on the level of CAPN1 expression in broiler chickens at the investigated stage of ontogenesis.