Background: The clinical appearance and biologic behavior of drug- induced pemphigus depend on the type of inducing drug. Objective: Our purpose was to investigate patients with drug-induced pemphigus vulgaris and pemphigus foliaceus antigens and compare results of studies to detect antibody reactivity in sera of these patients with the serology of patients with idiopathic pemphigus. Methods: Ten patients with drug-induced pemphigus were studied. Antibody reactivity was determined against the pemphigus vulgaris antigen, desmoglein 3, and against desmoglein 1. Results: The patient with pemphigus foliaceus and low levels of autoantibodies precipitated neither antigen. One patient with pemphigus vulgaris and high levels of antibody also failed to precipitate any specific antigen. Sera from eight patients with drug-induced pemphigus vulgaris had circulating autoantibodies directed to either the pemphigus vulgaris or pemphigus foliaceus antigen. Low levels of antibody in two of these eight patients precipitated only the pemphigus foliaceus antigen. High levels of antibody in five of the eight patients precipitated the pemphigus vulgaris antigen; two of these also reacted with the pemphigus foliaceus antigen. Conclusion: The autoantibody response was similar in both spontaneous and drug-related disease. A similar molecular mechanism in the two types of pemphigus is suggested.