Significance Whereas T cells are known to recognize peptides, vitamin B metabolites, or lipid antigens, we identify several nonlipidic small molecules classified as pentamethylbenzofuransulfonates (PBFs) that activate a population of CD1d-restricted natural killer T (NKT) cells. This represents a breakthrough in the field of NKT cell biology. This study also reveals a previously unknown population of PBF-reactive NKT cells in healthy individuals with stereotyped receptors that paves the way for future studies of the role of these cells in immunity, including sulfa drug hypersensitivity.