Experimental furunculosis caused by Aeromonas salmonicida was induced in rainbow trout (Oncorhynchus mykiss Walbaurn, 1792) using intraperitoneal injection and immersion challenge methods. A total of 65 (50 experimental and 15 control) rainbow trouts (weight 155 +/- 15 g and 20-25 cm in size) were used for this experimental work. Aeromonas salmonicida at a concentration of 3x10(5) cfu/ml (0.1 ml per fish) was intraperitoneally injected to twenty-five fish (first group). A second group of 25 fish was immersed in 30 I water inoculated to which 3 ml of bacterial inoculum (3x10(5) cfu/ml) had been added for one hour. Sterile saline solution (0.1 ml/fish) Was intraperitoneally injected to control group. Necropsy of the fish was performed, macroscopic and microscopic findings were evaluated. The chronic form of disease was observed in both groups. Anorexia, irregular swimming, hemorrhages at the dorsal, ventral and pectoral base of fins were the main clinic and macroscopic findings. However, in some fish, diffused or focal scale eruption on the dermis from operculum to caudal fin, periocular hemorrhages and exophtalmos were observed. Similar microscopic findings were determined in the both experiment groups. Microscopically, foci of bacteria with no inflammatory response especially in the muscles, gills, heart, stomach, pyloric caeca, intestines, kidney. spleen and liquefactive necrosis in the muscles were the main microscopic findings.