Abstract.The sensitivity of the immunoperoxidase (IP) and fluorescent antibody (FA) techniques applied to frozen sections of organs of carp infected with spring viraemia virus (SVCV) was similar, both in respect of the intensity of the reaction and in the detection rate of the antigen. Seven days after a waterborne infection both methods detected the antigen in the kidneys and to a lesser extent in the liver and spleen. Quantification of virus gave a titre of 102.8to 105.5TCID50/g of kidney, whereas the agent could not be isolated from liver and spleen tissue. In contrast, at 241/2days post–infection the viral antigen could be readily detected in liver and spleen but only occasionally in the kidneys using the IP and FA techniques. At this time, liver and spleen showed infectivity titres of 103.8to 107.2TCID50/g tissue, whereas the kidneys were found to be free of infective virus. It is concluded that using the IP and FA techniques SVCV can be detected most frequently in the kidneys from 7 to 14 days post–infection and in the liver and spleen from 14 to 24 days post‐infe