Follicular lymphoma shows a wide geographic variation in incidence, occurring more frequently in the U.S. than in Japan. A translocation involving the bcl-2 gene on chromosome 18 and the immunoglobulin heavy chain gene on chromosome 14 is frequently found in follicular lymphomas and is believed to play a critical role in the pathogenesis of these tumors. Recently, bcl-2/IgH rearrangements have been detected in reactive lymphoid tissue obtained from European patients, indicating that such rearrangements occur at some low but measurable background rate. In non-malignant tissues, the polymerase chain reaction was used to study the frequency of bcl-2/IgH rearrangements in reactive lymphoid tissue obtained from American and Japanese patients to find out whether geographic variation in the incidence of follicular lymphoma was caused by differences in sporadic occurrence of the t(14;18). We found such rearrangements in 5 of 15 American hyperplastic tonsils and lymph nodes and 5 of 10 Japanese tonsils, an incidence close to that previously seen in European patients. These data suggest that the background incidence of such rearrangements is similar in all populations, regardless of the incidence of follicular lymphoma.