We examined the chemiluminescence response of peripheral blood monocytes from patients with cystic fibrosis (CF) and their asymptomatic parental carriers of the CF gene to three different types of stimulation. We found that monocytes from both patients and carriers have increased luminol-dependent chemiluminescence in the first 25 min after stimulation by adherence to glass. These results are consistent with the hypothesis that monocytes from both CF heterozygotes and homozygotes respond to adhesion with increased oxygen radical formation. The increased adherence-induced monocyte chemiluminescence of the parental carriers did not vary with age or length of exposure of the parents to a child with CF. Also, repeated exposure to medications and respiratory secretions of CF patients was not associated with an increase in adherence-induced monocyte chemiluminescence of their nonbiologically related caretakers. Thus, this observed increase in chemiluminescence is not simply secondary to the medications or respiratory dysfunction seen in the patients with CF. Patients with other types of obstructive lung disease did not show increased adherence-induced monocyte chemiluminescence. We conclude that increased early phase adherence-induced monocyte chemiluminescence occurs in patients with cystic fibrosis and the obligate carriers of the CF gene independent of environmental influences.