Immunization of rabbits and rhesus monkeys with Streptococcus mutans whole cells, cell walls, and defined streptococcal antigens (SAs) SA I/II, SA I, and SA II resulted in high antibody titers to SA I/II (10(-4) to 10(-6)) when tested by the solid-phase radioimmunoassay. Cross-reactive antibodies to heart homogenates (HH) were not elicited in rhesus monkeys. A few rabbits immunized with cell wall or SA II preparation in Freund complete adjuvant followed by the incomplete adjuvant yielded low antibody titers (up to 10(-2)) to the HH. The specificity of the putative heart cross-reactive antibodies was tested by immunoadsorption with related and unrelated antigens. Whereas antibody to SA I/II showed specific adsorption with SA I/II but not with HH, immunoglobulin G, or the unrelated antigens, antibody to HH seemed to have been adsorbed with all of the related and unrelated antigens. There was no evidence for the development of heart cross-reactive antibodies on immunization of rhesus monkeys or rabbits with SA I/II and aluminium hydroxide or Freund incomplete adjuvant, administered by the subcutaneous or intramuscular route in doses of up to 13 mg of the immunogen.