Pigment depositions in fillet and internal organs represent a costly problem to Norwegian aquaculture industry. In the worst cases, the production quality of up to 20% of fillets from certain farms is affected, and this implies trimming, cassation and sub sequently extra production costs. In a pre-project financed by FHF, we have estimated the problem to affect 4% of the total salmon production in Norway, implying a loss of 2000 tons annually. The condition seems to be associated with vaccination, and we h ave shown that the dark-coloured changes in fact are inflammatory sites with accumulation of pigmented cells or so-called melanomacrophages. In previous works, we have in addition cloned the genes for melanin production in salmon and have identified a sal mon leukocyte cell-line to be melanin-producing. These results provide unique tools to investigate the reasons for undesired melanin production in salmon. The overall goal for this project is to identify preventive measures so that the condition and subse quent losses may be avoided. Surprisingly, melanin-producing leukocytes also seem to harbour functions related to mammalian dendrtitic cells, making them most interesting for future vaccine development. The project is a follow-up to the pre-project "Pigme nt spots in the musculature and organs of the Atlantic salmon" granted Dr. E. O. Koppang by Fiskeri- og havbruksnæringens forskningsfond (FHF). The industry is much aware of the problems, and the current application is supported by the two of the leading companies in vaccine producution and salmon farming; Intervet Norbio and Marine Harvest.