Fish Pasteurellosis first appeared in the Mediterranean area in 1990 causing heavy losses in fish-farms and affecting also the open sea. From 1990 to 1993 our laboratory diagnosed 201 Pasteurellosis outbreaks, of which 53.7% were Dicentrarchus labrax, 23.9% Mugilidae, 17.4% Sparus aurata, 2.4% Atherina spp., 0.9% Pagrus major, 0.9% Dentex dentex, 0.5% Solea solea. Diseased fish present locomotor ataxy, dark colouring and respiratory problems. Necropsy shows haemorrhagic petechia on many tissues and organs and congestions in the intestines, which contained mucous faeces. Moreover fish are afflicted by splenomegaly, with small whitish nodules also in the liver and kidney parenchym. Diagnosis has been effected through traditional isolation and identification of Pasteurella in cultured and indirected immunofluorescence from internal organs. The most used antibiotics are: Flumequine (orally 12 mg/kg b.w.) or Ampicillin (orally 20-30 mg/kg b.w. or in water 30-50 ppm for 3-5 days). Moderate sensitivity to Tetracycline and Chloramphenicol. A timely beginning of the therapy improve chances of survival. Four vaccination tentatives are under way: the first employs vaccines inactivated by formalin and containing various cell numbers, the second uses lipopolysaccharide of bacterial cell, the third only polysaccharide and lipid A extracted by acid hydrolysis and the fourth strains attenuated with the growth in media without 2 aminoacids.