Keyhole limpet hemocyanin (KLH) is a recently described immune stimulant and hapten carrier derived from a circulating glycoprotein of the marine mollusk Megathura crenulata. We previously reported that KLH has significant antiproliferative effects in vitro against breast, pancreas, and prostate cancers. We hypothesized that KLH would be effective against Barrett's esophageal adenocarcinoma in an in vitro model. Barrett's esophageal adenocarcinoma cell lines (SEG-1 and BIC-1) were cultured using standard techniques. Cells were plated at 1 x 10(5) and KLH was added at concentrations ranging from 400 ng to 100 microg/well. After 24 and 72 h incubation, cells were assayed for viability using the MTT technique. Statistical analysis was performed using ANOVA. Apoptosis was evaluated using a cell death detection kit after 16 hours of incubation with KLH. KLH treatment significantly (p < 0.001) reduced viability in a dose and time-dependent manner. Apoptosis was increased in treated SEG-1 cells, but no changes in apoptosis were seen in treated BIC-1 cells. KLH directly inhibits the growth of human Barrett's esophageal cancer in vitro by apoptotic and nonapoptotic mechanisms.