In this article we report a case of erythroblastic synartesis, a rare disease characterized by ineffective erythropoiesis, clusters of erythroblasts due to membrane invaginations, in which an autoimmune pathogenesis is hypothesized. We investigated the presence of anti-erythroblast autoimmunity in bone marrow cultures using a mitogen-stimulated direct antiglobulin test, a method reported to be able to disclose a latent autoimmunity in various diseases. The test revealed the presence of erythroblast-bound IgG, supporting the hypothesis of the autoimmune pathogenesis of erythroblastic synartesis. Supernatants induced the same specific morphological features, i.e erythroblastic clustering and diserythropoietic signs (multiple nuclei, nuclear inclusions, and intercellular bridges) in normal progenitors.