Pemphigus vulgaris is characterized by bound and circulating IgG antibodies to an epithelial antigen, antibody binding resulting in acantholysis. This study examines the role of pemphigus serum in the initiation and perpetuation of acantholysis. Oral epithelial cells derived from a patient with pemphigus vulgaris were cultured in vitro in the presence of normal serum. Also, normal oral epithelial cells were cultured in pemphigus serum for between 0.5 and 72 h or exposed to pemphigus serum for 72 h and then cultured in normal serum for 2 wk. Oral epithelial cells from the pemphigus patient continued to display acantholysis for the 3-wk duration of the culture. Normal oral epithelial cells showed acantholysis within 30 min exposure to pemphigus serum and the acantholysis persisted in the cultures, pulse exposed to pemphigus serum, for the duration of the explant culture. These results support the notion that pemphigus serum is directly responsible for acantholysis which may then be persistent.