Recovery of internal tags during the filleting process would create new possibilities for tagging experiments on several species, in Norwegian fisheries primarily cod, haddock, saithe, herring and mackerel. In connection with a program for developing a detector and a devise for recovery of internally tagged fish, laboratory experiments with tagging of young saithe were carried out. The results of the saithe tagging experiment showed that after six weeks about 75% of the tags were encapsulated by tissue without any signs of infection or disease. Later, apparently no more tags were encapsulated. Approximately one third of the non-encapsulated tags were extruded. The growth of the tagged fish was significantly lower than for the untagged fish.