Naegleria fowleri is the cause of primary amoebic meningoencephalitis in man. The mouse is considered to be a suitable experimental model for this disease. The data presented shows that blood neutrophils from N. fowleri immune mice (immunised) that had received a 'recall' amoeba antigen had altered responses compared with those from similarly treated normal mice. The neutrophils from immune animals showed increased basal levels of oxygen-dependent respiratory activity, measured by the chemiluminescence response. These neutrophils also showed increased responses to formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), phorbol myristate acetate (PMA), and opsonized N. fowleri. The results are consistent with previous data suggesting that the neutrophil (and its activation) is important in defence against N. fowleri.