Background: Several assays are available to detect pemphigus antibodies. The most commonly used are indirect immunofluorescence (IIF) and immunoblotting (IB). Objective: Our purpose was to compare the sensitivity of these assays in detecting pemphigus antibodies. Methods: Fifty-two sera from 41 patients with pemphigus vulgaris (PV) and 22 sera from 18 patients with pemphigus foliaceus (PF) were tested concurrently for the presence of pemphigus antibodies. The IIF studies were conducted with two different substrates: monkey and guinea pig esophagus. Results: Pemphigus antibodies were detected with equal sensitivity by IIF in patients with PV and PF (i.e., positive in 87% and 86% of sera, respectively). By contrast, IB assay was much less sensitive in PF than in PV (i.e., positive in 45% vs 83% of sera, respectively). The antibodies in PV generally reacted more strongly against monkey esophagus, whereas those in PF reacted more strongly against guinea pig esophagus. All patients with intercellular antibodies that reacted more strongly against monkey than guinea pig esophagus had PV, whereas all those with intercellular antibodies that reacted more strongly against guinea pig than monkey esophagus had PF. Conclusion: IIF is a more sensitive assay than IB for detecting antibodies associated with PF. The substrate specificity of the antibodies provides a simple means to distinguish between PV and PF. (J Am Acad Dermatol 1997;37:211-6.)