The ability of ε-amino caproic acid (EACA)-treated normal serum and of cystic fibrosis (CF)-affected and carrier sera to promote the release of lysosomal enzymes from sensitized human polymorphonuclear leukocytes (PMN) was assessed through the measurement of β-glucuronidase and myeloperoxidase acitivity after exposure of these cells to the various test sera. This study was initiated to extend the analogies between preciliary dyskinesia factor (pre-CDF), separated from the cell-free media of cultures derived from CF homozygous and heterozygous individuals, and C3a anaphylatoxin. The extent of lysosomal degranulation of human PMN exposed to fresh untreated sera of each of five controls, seven CF homozygotes, and eight heterozygotes, as expressed by the amount of,β-glucuronidase released, was 7.84% (± 0.934) for control sera, 14.01% (±1.79) for CF-affected sera, and 10.61% (±1.43) for heterozygous sera. The difference between CF homozygotes and control subjects is significant (P <0.001), as is the difference between CF-affected and carrier individuals (0.001 < P < 0.005) and between control subjects and carriers (0.001 < P < 0.005), when β-glucuronidase release is measured. Analogously, values of myeloperoxidase released by the three groups studied reflect differences similar to those of β-glucuronidase. However, the differences between control subjects and CF heterozygous individuals are not significant. Treatment of these sera with 1 M EACA gave values for β-glucuronidase and myeloperoxidase release which are slightly reduced when compared with those obtained with fresh, untreated samples. EACA apparently reduces the activity of β-glucuronidase released from PMN. Amicon filtration studies of these serum samples demonstrated that degranulating ability and the presence of ciliary dyskinesia, as assessed by rabbit tracheal bioassay, are not always associated. Therefore, the relationship between pre-CDF and the degranulator activity in native CF-affected and carrier sera is unclear, in part because of the limitations inherent in the test systems employed. The pathophysiology of CF can be explained by excessive degranulation of exocrine glandular cells, resulting in inspissation of their ducts. The finding of degranulator molecules in CF sera allows for a test of this hypothesis. The possibility exists that this degranulating activity, as well as the molecules responsible for ciliary dyskinesia, whether they are the same or different molecular species, may represent an excess of normal products. These molecules, related to C3a anaphylatoxin and/or kinins, are present in excess in CF because of the deficiency of an enzyme which normally controls their level by inactivation.