behaviorally conditioned immunosuppression o-f a primary humoral immune response was investigated in both the sexes of five selectively bred lines of rats. in the experimental group, an illness-induced taste aversion was produced by pairing sucrose (cs) and cyclophosphamide (us), an immunosuppressant that induces gastrointestinal distress. a nonconditioned group received water as the cs and cyclophosphamide (cy) as the us while a placebo group received sucrose as the cs and isotonic saline as the us. three days following the cs-us pairing, the animals received an injection of sheep erythrocytes (srbc). a hemagglutinating antibody titer was used to assess the humoral antibody response (cr) six days later. overall, there was evidence of behaviorally conditioned immunosuppression. taste aversion was present 24 hours following conditioning in the mr/har/lu (p<.01), mnr/har/lu (p<.05), shs (p<.01) and rla/lu (p<.01) lines with persistant extinction in mnr/har/lu animals and the appearance of taste aversion in the rha/lu (p<.05) animals 48 hours following conditioning. results are discussed on behavioral and biochemical levels with a conclusion emphasising the importance of research in behavioral immunology and calling for greater attention to the field.