A group of 49 multiple myeloma patients, 20 men and 29 women, were evaluated. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), 17 beta-oestradiol (E) and testosterone (T) serum concentrations have been detected by radioimmunoassay. Peripheral blood lymphocyte proliferation in response to phytohaemagglutinin (PHA), concanavalin A (ConA), recombinant interleukin-2 (rIL-2) and dextran sulphate (DxS) was investigated. Our findings provide evidence for two different patterns of sex hormone changes and immune dysfunctions presented differently by male and female multiple myeloma patients. In men increased FSH, LH and E concentrations and an augmented E to T ratio were associated with decreased lymphocyte blastogenic response to PHA, ConA and increased proliferation to rIL-2 and DxS. Female patients with multiple myeloma demonstrated normal values of FSH, LH and T, but a diminished E level and decreased E to T ratio correlated with a lymphocyte normal response to PHA and ConA and augmented blastogenesis to IL-2 and DxS. Our data, while admittedly preliminary, suffice to provide an indication of sex hormone changes in multiple myeloma patients, which could be responsible, at least in part, for the immune dysfunction observed in multiple myeloma.