Experiments were performed to evaluate the luminol-dependent chemiluminescent (LDCL) responses of neutrophils from clinically normal calves and calves challenged with 'Pasteurella haemolytica' A1 using opsonized zymosan (OZ) and phorbol myristate acetate (PMA) as agonists. In the first experiment, the LDCL responses of neutrophils obtained by bronchoalveolar lavage (BAL) from ten clinically normal 3-4 month old Holstein calves were compared to blood neutrophil LDCL responses from the same animal. The BAL neutrophils LDCL responses, when stimulated with OZ, were significantly greater than those of blood neutrophils from the same animal and correlated positively with the number of BAL neutrophils in the lavage. In the second experiment, the LDCL responses of BAL neutrophils from six calves challenged with 'P. haemolytica' A1 were compared to responses of BAL neutrophils from six unchallenged calves and to blood neutrophils from calves within the same experimental group. The calves were evaluated on 4 experimental days, 3 days prior to challenge (Day -3), 4 hours post-challenge (4hPC), 3 days post-challenge (Day 3) and 6 days post-challenge (Day 6). For both groups, suppression of LDCL was observed on Day 3 with both agonists (p < 0.05). This was greater for OZ stimulation (19 ± 10% of Day-3 100%) than for PMA (59 ± 21% of Day-3 100%). When the LDCL responses of BAL and blood neutrophils were compared within each group, the BAL neutrophils from the challenged calves demonstrated a higher total LDCL response to OZ on each day except Day 3 when the responses approximated those of the blood neutrophils' (BAL neutrophil LDCL = 124.8 ± 48.5 mV min, blood neutrophil LDCL 134.5 ± 76.3mVmin). Blood neutrophil LDCL responses did not differ between groups.