Three clonally related lymphoma lines (Mac-1, Mac-2A and Mac-2B) derived from progressive stages of CD30+ cutaneous T-cell lymphoma were found to constitutively secrete GM-CSF. The secretion of GM-CSF was identified by the ability of cell line supernatants to stimulate growth of megakaryoblastic cell line M-07e. This supernatant-mediated stimulation was inhibited by anti-GM-CSF MoAb (>98% inhibition for Mac-1 and Mac-2B lines, and >95% for Mac-2A line). Synthesis of GM-CSF was confirmed, at the mRNA level, by reverse transcriptase PCR and, at the protein level, by ELISA. Quantification of GM-CSF in supernatants by ELISA showed that the Mac-1 line, derived from an early, clinically indolent stage of the lymphoma, produced much more GM-CSF (>1600 pg/ml) than Mac-2A and Mac-2B lines which were derived from a late, aggressive stage (30-50 and 50-120 pg/ml, respectively). Lack of inhibition of cell growth by anti-GM-CSF MoAb as well as lack of response to exogenous GM-CSF of cells cultured at low concentration have demonstrated that GM-CSF does not act directly as a growth factor for these lines. ELISA studies showed that GM-CSF concentration in serum and urine of the patient were not elevated (<5 pg/ml). From several other cell lines tested (two primary CD30+ ALCL, 2 CD30- non-lymphoblastic T-cell lymphomas and 4HD), only two HD lines with a T-lymphocyte phenotype secreted detectable amounts of GM-CSF. Our data show that cells lines from a patient with cutaneous T-cell lymphoma constitutively secrete GM-CSF, although this capacity is relatively diminished in lines developed from more advanced disease.