Anti-ceramide monoclonal antibodies detect sphingomyelinase-induced increase in surface ceramide. Hela cells were treated with the indicated concentrations of Bacillus cereus sphingomyelinase for 30 min. After fixation with PFA, coverslips were labeled with 15B4 anti-ceramide monoclonal antibodies for 1 h followed by secondary antibodies. Ceramide labeling is shown in red. Bars, 20 µm. These results are representative of three independent experiments.