Immunoglobulin levels were followed in 21 nonsteroid-dependent asthmatics who required corticosteroids for an exacerbation of asthma. Twenty subjects who did not receive corticosteroids were used as controls. Baseline IgM and IgE levels were significantly higher in the corticosteroid-treated group. A fall in IgG level, maximal at 2 to 4 wk, was observed in the corticosteroid group, but not in control patients. Similarly, a significant fall in IgA was observed only in the corticosteroid group, maximal at 6 to 8 wk. There was no significant change in IgM levels in either group. Total IgE levels increased dramatically 1 wk after institution of corticosteroids. This was followed by a decrease to baseline or below at 6 to 8 wk. Changes in specific IgE antibody titers as measured by RAST technique revealed similar changes to those seen with total IgE. The results of the study indicate that asthma therapy with short-term corticosteroids can be associated with prolonged depressions of serum IgG, IgA levels and transient elevations of IgE levels, without apparent alterations of IgM levels.