Development of eosinophilia was studied in four strains of guinea pigs (gp), selectively bred for either high or low respiratory anaphylactic reactivity. One high‐asthma strain (IMM/S 209) and one low‐asthma strain (IMM/R 203) developed spontaneous high blood eosinophilia. The 2 other gp strains ‐ one high‐asthma strain (IMM/S 740) and one low‐asthma strain (IMM/R 201–16) – maintained normal low levels of eosinophilic granulocytes (eos). The levels of eos in various tissues showed similar differences between the gp strains. Following immunization with ovalbumin/Al(OH)3the levels of blood eos increased significantly only in gp of strain 209. The blood eos levels in gp of all 4 strains decreased significantly following immunization with ovalbumin in Freund's complete a