Two workers from the same factory presented to the same emergency department within six weeks of one another with moderate (Case 1) and severe (Case 2) methemoglobinemia. Subsequent investigation revealed that the factory produces phenylpropanolamine and that both patients, shortly before becoming ill, were inadvertently exposed to methyl nitrite, a critical reagent in this production. Although other nitrites induce methemoglobinemia, exposure to methyl nitrite during phenylpropanolamine production appears to be a new cause of occupational methemoglobinemia.