Growth hormone (GH) treatment is known to increase milk yield but the underlying molecular mechanisms are largely unknown. The objective of this study was to profile changes in milk protein gene expression resulting from GH administration to lactating dairy cows. GH increased milk yield by 32% with concomitant increases in protein, fat and lactose yield. Milk composition was unaffected by treatment. Similarly, GH-treatment increased yield but not concentration of all major individual milk proteins. Expression of the key milk protein genes was not consistently regulated suggesting effects of GH at both transcriptional and post-transcriptional levels in the bovine mammary gland.