t(11 ; 18)(q21 ; q21) is a specific chromosomal aberration in mucosa-associated lymphoid tissue (MALT) lymphoma, and produces chimeric transcript Apoptosis Inhibitor 2 (API2)-MALT1. Although it is known that API2 has an antiapoptotic effect, it is still unclear whether this also applies to API2-MALT1. To investigate its effects against various apoptotic stimuli, API2-MALT1 was expressed by means of retroviral infection on the epithelial cell line HeLa and the murine Pro-B cell line Ba/F3. On both these cell lines, API2-MALT1 was found to cause a significant reduction in UV-induced apoptosis. The apoptosis induced by doxorubicin was also inhibited by API2-MALT1, but not that induced by IL-3 withdrawal from Ba/F3. These findings suggest that API2-MALT1 has an antiapoptotic effect on both epithelial and lymphoid cells and that this effect depends on the apoptotic stimulus.