Immature sockeye salmon (Oncorhynchus nerka) responded to the intraperitoneal injection of heat-killed, adjuvant-suspended cells of the salmonid kidney disease bacterium by producing agglutinins specific for the pathogen. These antibodies were detectable for at least 16 months following a single injection. With water temperatures of 12–15 C which prevailed during the first 100 days following this injection, the response was rather slow to develop, and whether or not antibodies were produced in this period, depended on the dose of antigen given. Under a similar temperature regime, a second injection, given 13 months after the first, elicited a clear-cut anamnestic response. Ninety days following primary and secondary vaccination, maximum agglutinating titres were 1:2,560 and 1:10,240, respectively.

Electrophoregrams of sera from vaccinated fish revealed the presence of one, and sometimes two, fractions of low mobility. These fractions occurred in the gamma and beta regions, and contained antibody. They were most distinct in sera with high titres; they were not observed in sera from non-vaccinated controls (these typically showed three major components of higher mobility); and they were selectively removed when sera were adsorbed with cells of the kidney disease bacterium. Some properties of the antibodies were studied.