Samples from eight organs, i.e. gills, liver, brain, head kidney, spleen, thymus, white muscle and posterior intestine, were dissected out and immediately frozen in cryo tubes in liquid N and stored at -80°C before RNA extraction. The RNA extracted from three spleen and four head kidney tissue samples were of low quality, and we had to redo the sampling from four individuals, These tissue samples Stability of six genes in gills of Atlantic salmon during smoltifi-cation calculated with the geNorm software were stored on RNA later (Ambion) at -20°C before further processing.