Heat stress is a key factor that negatively affects livestock productive and reproductive performance. A genome-wide scan was performed on a sample of 1,592 Italian Holstein bulls using 2 different measures of heat tolerance for milk yield and protein percentage. The first was a temperature-humidity index breeding value (THI EBV) recently proposed for the Italian Holstein breed. The latter was obtained by a principal component analysis carried out on milk test-day records corrected for environmental effects except for THI. Only the second principal component (PC2), which describes the individual patterns of corrected production data across different THI levels, was considered. Animals were genotyped with the Illumina BovineSNP 50 BeadChip. Monomorphic SNPs (7,140) and SNPs with a call-rate <95% (1,045) were discarded. In total, 45,546 SNPs were retained for the analysis. All bulls had a THI EBV, whereas the PC2 was available only for a sub-sample of bulls (423). Genome-wide scan was performed fitting the GRAMMAR approach through the GenABEL R package. Then, a Gene discovery analysis was carried out considering windows of 0.5 Mb surrounding the significant marker (0.25Mb up and down stream respectively). No significant associations were detected for milk THI EBV, apart from a weak signal on BTA 2 at about 32 Mb. In this region is located the solute carrier family 38, member 11 (SLC38A11) gene, reported to be involved in folliculogenesis in cattle. For PC2, 3 SNPs were detected on BTA 6, 16 and 26, respectively. The SNP on BTA26 is located in a region that hosts genes involved in the ovarian activity (FGF8). An interesting candidate for the SNP located on BTA16 at approximately 42.1 Mb is the dehydrogenase/reductase member 3 (DHRS3), involved in the embryonic development in humans. No significant associations were found for protein percentage THI EBV. However, 3 significant markers were detected for PC2 on BTAs 20, 14 and 8. Interestingly the BTA14 region hosts the junctophilin 1 (JPH1) gene, whose expression has been found to be upregulated in the hypothalamus of chickens subjected to heat stress. These preliminary findings suggest potential genomic regions linked to heat stress resistance in dairy cattle.