A luminol‐enhanced chemiluminescence (CL) technique was developed for porcine pulmonary alveolar macro‐phages (PAM) and polymorphonuclear cells (PMN). PAM were obtained from lung washings of 3 week old gnotobiotic pigs. PMN were obtained from peripheral blood by separation on a discontinious Percoll gradient. Optimum CL signals were obtained with 105PAM/tube and 5X104PMN/tube. Stimulation indexes (SI) for PAM were approximately 10 for phorbol myristate acetate (PMA), 8 for opsonizedActinobacillus pleuropncumoniaeand 3 for opsonized zymosan. SI for PMN varied from 100 to 180 for complement opsonized zymosan, from 50 to 100 for opsonizedA. pleuropneumoniaeand from 10 to 20 for PMA. Formyl‐methionyl‐phenylalanine and calcium ionophore A23187 did not stimulate the oxidative activity of PAM or PMN. PAM that had been frozen and stored in liquid nitrogen reacted as freshly obtained PAM in the CL assay; however, PMN that had been frozen lost a great deal of their ability to produce oxygen radicals after thawing.