Hu, X., Lü, A., Chen, H., Gao, X., Xu, H., Zhang, C., Fang, X. and Lei, C. 2009. Preliminary evidence for association of prolactin and prolactin receptor genes with milk production traits in Chinese Holsteins. J. Appl. Anim. Res., 36: 213–217. Genetic polymorphisms of prolactin (PRL) and prolactin receptor (PRLR) genes in Chinese Holstein cattle were detected by PCR-SSCP methods. Polymorphisms were observed in both genes and direct sequencing confirmed the A>G mutation at position 8398 in exon 4 of PRL gene and the A>C mutation at position 7866 in intron 9 of PRLR gene. The frequencies of allele A/B and C/D were 0.894/0.106 and 0.781/0.219 for PRL and PRLR genes, respectively. Chinese Holstein cows with genotype BB were observed to be higher milk yielders than genotypes AA and AB (P<0.05). It is concluded that the polymorphism in the PRL gene may be a genetic marker in breeding for milk yields in Holsteins, but further validation is required.