Eighteen patients with melphalan refractory myeloma were treated with vindesine and prednisone. Plasma spermidine concentrations were measured by radioimmunoassay before and after a single vindesine injection. Seven patients showed a significant rise of plasma spermidine after vindesine and five of these showed a clinical response on further evaluation. Of the 11 patients who did not show raised spermidine concentrations, 10 did not respond to the therapy. The correlation between clinical response/rise of spermidine and between non-response/no rise of spermidine was statistically significant (p less than 0.05). Pretreatment spermidine concentrations did not distinguish those who responded to treatment nor did they differ in patients and controls.