A survey was conducted on the effects of volcanic ash from Mount Saint Helens on the humoral immunologic parameters of loggers. The cohort consisted of 464 active, healthy loggers employed in logging camps located in the ash fall area. The comparison group consisted of 234 active loggers of similar job distribution from logging camps in Oregon that were outside the ash fall area. Both groups were matched as to age, ethnic background, and smoking. The serum concentrations of the immunoglobulins (IgA, IgC, and IgG), complement components (3 and 4), and the antinuclear antibody (ANA) were assayed by solid phase fluorescence immunoassay 5 weeks after the May 18, 1980 volcanic eruption. The assays were repeated 1 year later to determine the effects of long term exposure to volcanic ash. Complement component titers were significantly lower at both times in the exposed loggers compared to comparisons. No significant differences between the two groups were observed for the immunoglobulin or ANA titers at either time. However, the loggers from the ash fall area showed a distinctly lower average IgC concentration after 1 year of exposure when compared to the 1980 baseline value. IgA concentrations increased in the exposed group compared to the 1980 baseline. The authors suggest that some of the changes in the humoral immunity factors may be related to the presence of free silica (14808607) in volcanic ash.