The bovine prolactin (PRL) and bovine growth hormone (bGH) genes exhibit several polymorphisms.Some of them can be detected by molecular techniques using restriction endonucleases, such as RsaI for the PRL gene and MspI for the bGH gene.We examined the relationship between the PRL-RsaI and bGH-MspI polymorphisms and some economically important characteristics of Holstein cows.Research was conducted on 315 Holstein cows from 5 municipalities in the Department of Antioquia, Colombia.Individuals were genotyped using PCR/RFLP.The statistical analysis was carried out using generalized linear models and a regression analysis.Polymorphism of the bGH gene was found to have a significant association with the percentage of protein in milk and milk yield.Genotype (-/-) was favorable for dairy yield, while genotype (+/+) was favorable for protein percentage.The PRL gene showed no significant association with any of the evaluated characteristics.The bGH gene appears to be a candidate for the implementation of marker-assisted selection programs.To determine the effect of the prolactin gene, research should ©FUNPEC-RP www.funpecrp.com.