Although studies have established that exogenous growth hormone (GH) treatment stimulates growth in fish, its effects on target tissue gene expression are not well characterized. We assessed the effects of Posilac® (Monsanto, St. Louis, MO), a recombinant bovine GH, on tissue transcript levels in rainbow trout selected from two high growth rate and two low growth rate families. Transcript abundance was measured in liver and muscle using the GRASP 16 K cDNA microarray. A selection of the genes identified as altered using the microarray, and transcripts for insulin-like growth factors, growth hormone receptors (GHR) and myostatins were measured by real-time PCR in the liver, muscle, brain, kidney, intestine, stomach, gill and heart. In general, transcripts identified as differentially regulated in the muscle on the microarray showed similar directional changes of expression in the other non-hepatic tissues. A total of 114 and 66 transcripts were identified by microarray as differentially expressed with GH treatment across growth rate for muscle and liver, respectively. The largest proportion of these transcripts represented novel transcripts, followed by immune and metabolism-related genes. We have identified a number of genes related to lipid metabolism supporting a modulation in lipid metabolism following GH treatment. Most notable among the growth axis genes measured by real-time PCR were increases in GHR1 and-2 transcripts in liver and muscle. Our results indicate that short-term GH treatment activates the immune system, shifts the metabolic sectors and modulates growth regulating genes.