Non-Hodgkin's lymphoma (NHL) is the third most rapidly increasing cancer in the United States. HIV-related NHL is responsible for some of the increase since the early 1980s. However, it cannot explain the steady increase in the incidence rates in earlier years, nor the entire increase shown recently. A possible role of environmental exposures is receiving attention. One possibility is that exposure to organochlorines (OCs) may be related to the occurrence of NHL. NCI is currently designing a large population-based case-control study to investigate this hypothesis further by analyzing OC levels in blood collected at the time of interview from cases of NHL and their matched controls. At the time of these interviews, cases in the main case-control study would most likely have already received chemotherapy. If chemotherapy changes the blood levels of OCs, this may lead to misclassification of exposure among cases and eventually to biased risk estimates. The purpose of this pilot study is to estimate the bias due to measuring the serum levels of OCs in cases during or after chemotherapy. Twenty newly diagnosed patients will be recruited for the study. From each patient, four consecutive blood samples, one prior to, two during, and one after chemotherapy, will be collected. Forty pairs of pre-existing cryopreserved serum samples (pre- and post-treatment) taken from the NHL patients who participated in an earlier NCI clinical study will also be included in this study. Samples will be assayed for OC levels. The results will be used to plan and to interpret another large case-control study (the main study).