The capacity to detect t(14;18) breakpoints in non-Hodgkin's lymphoma (NHL) peripheral blood and bone marrow was studied by DNA PCR. We studied 33 patients with follicular lymphoma (FL) (Working Formulation subtypes B, C, D) and 38 patients with intermediate-grade NHL (subtypes F, G). In the FL subgroup, 86% of the morphologically-positive bone marrow patients had amplifiable t(14;18) breakpoints by PCR. Remarkably, of 19 FL patients with 'negative' bone marrows, 11 (58%) were PCR-positive. In addition, half of the early clinical stage patients (I and II) had detectable breakpoints in their bone marrow DNA. Samples from NHL patients with intermediate-grade disease exhibit the same phenomena but at a considerably lower frequency. Paired peripheral blood and bone marrow samples were available at diagnosis in a subset of 56 patients. The concordance between bone marrow and peripheral blood PCR findings was high, with peripheral blood of 55/56 showing the same PCR results as the corresponding bone marrow.