Serum electrophoresis patterns and various measures of specific and non-specific immune competence were determined in 16 patients with paracoccidioidomycosis, at time of diagnosis and 6 mo. after therapy. The results were compared with those furnished by the study of 16 control subjects, matched by age and sex. Once treated, the patients approached normality in some parameters. Untreated patients had significantly diminished albumin levels with increased .alpha. 1, .alpha. 2 and .gamma. fractions. Ig[immunoglobulin]G was elevated and remained so during therapy. Before and after treatment patients had diminished total numbers and decreased percentages of E [erythrocyte] rosettes; they also had depressed lymphocyte transformation with phytohemagglutinin (PHA) and paracoccidioidin (P). Untreated patients exhibited the lowest skin test responses to PHA, purified protein derivative (PPD), P and candidin (C); significant differences, however, were limited to the former 2 antigens. All untreated patients had detectable antibody titers against Paracoccidioides brasiliensis; these titers had a tendency to drop during treatment. No direct correlation was found between elevated serum fractions, presence of antibodies and depressed cellular immunity.