Shigella flexneri 2a was isolated from a patient with Reiter's syndrome (RS) following a family outbreak of traveler's diarrhea. Among 3 members at risk, only the patient was positive for HLA-B27. Data from 3 similar families support the hypothesis that susceptibility to RS is genetically transmitted. It is urged that every effort be made to culture and subtype Shigella and other enteric pathogens in RS following diarrhea. Concurrently, the patient had hepatitis, interpreted as a parallel enteric infection.