We investigated the potential of ten cytokines (IL2, IL3, IL4, IL6, IL10, IL13, G-CSF, GM-CSF, interferon alpha, interferon gamma) and all-trans-retinoic acid to modulate the spontaneous proliferative response in vitro of purified B-non Hodgkin's lymphoma cells of various histological subtypes. 19 malignant lymph nodes were studied. In each case the growth could be influenced by several of these modulators. Cytokines most often implicated were interferon gamma (14/19 cases, 73.7%), IL4 (13/19 cases, 68.4%), interferon alpha (12/19 cases, 63.1%). IL2 (9/19 cases, 47.3%), IL6, IL10, IL13 and ATRA were less frequently involved (6/19 cases, 31.6%) and hematopoietic growth factors (IL3, GM-CSF, G-CSF) were rarely implicated (2/19 cases, 10.5%). The values of growth stimulation ranged from a 1.1-fold to a 6.1-fold increase, and the values of growth inhibition ranged from 15% to 98%. Each cytokine could be either inhibitory or stimulatory depending on the sample analyzed, and no relationship could be found with the histological subtype. Two notable exceptions were IL2, displaying exclusively a positive effect, and ATRA displaying exclusively a negative effect. Overall, these results may have strong implications for future clinical studies using cytokines in the treatment of lymphomas. Ideally, the pattern of in vitro growth response to cytokines or ATRA should be determined individually before undertaking any cytokine treatment.