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To evaluate in serial gallium-67 scans (GS) the role of semiquantitative tumor-to-background (Tm/Bg) and tumor-to-liver ratios in assessing response rates to chemotherapy, in Hodgkin's disease and non-Hodgkin's lymphoma.Twenty-seven consecutive patients (15 Hodgkin's disease and 12 non-Hodgkin's lymphoma patients) with an average age of 30 (range, 5–60) years underwent GS at prechemotherapy, early chemotherapy (after first cycle), and postchemotherapy. Average tumor, background, and liver region of interest counts obtained and Tm/Bg, tumor-to-liver, and liver region to background ratios were derived for each patient on serial GS. All patients were assessed by visual and quantitative GS and followed up clinically for more than 7 years.At early visual GS, 70% (19 of 27) of the patients showed rapid response, 15% (four of 27) showed delayed response (negative at post-GS), and 15% showed no response. Mean early-GS Tm/Bg ratio of disease-free patients (1±0.04) was significantly different from relapsed (1.4±0.2) (P<0.025) and progressive disease (1.8±0.7) patients. A significant difference was noted (P<0.01) in serial paired comparisons of Tm/Bg ratios between pretherapy and early-therapy scans in relapsed patients, whereas progressive disease patients showed no significant change during the same time. At early-GS, 15 patients showed quantitative rapid response (Tm/Bg ratio 1.04), nine patients showed quantitative delayed response (Tm/Bg ratio >1.04 with significant serial change between pretherapy and early-therapy GS), and three patients showed quantitative no response (Tm/Bg ratio >1.04 with nonsignificant serial change between pretherapy and posttherapy GS).Quantitative GS is an effective tool in the detection of early response to chemotherapy. Quantitative response rates after the first cycle can more reliably identify patients who are most likely to be disease-free or relapse after first-line therapy or those that will show no response to therapy as compared with visual analysis alone.