To better detail the status of functional T cell subsets and natural killer cells in multiple myeloma, we undertook a detailed immunophenotypic study of circulating mononuclear cells in myeloma. We studied myeloma patients entered on a large prospective, randomized ECOG chemotherapy trial EST 9486 for patients with newly diagnosed multiple myeloma. All patients were studied prior to entry and then two months after initiation of therapy (e.g. post two cycles of Vincristine, BCNU, melphalan, cyclophosphamide and prednisone (VBMCP)). The chemotherapy protocol was a three-arm protocol utilizing either VBMCP, VBMCP alternating with interferon, or VBMCP with intermittent high dose cyclophosphamide. The major findings in this analysis include significant reductions in the white blood cell count, total lymphocytes, T cell (CD3+), T helper (CD4+), and T suppressor (CD8+) cells, after 2 cycles of VBMCP. However, there was a relative sparing of Natural killer (CD16+) and activated T cell (CD2+, HLADR+) reduction in these same patients. In summary, only two cycles of combination chemotherapy resulted in significant reductions in white blood cell and lymphocyte counts in multiple myeloma patients. All cell types appear to have been reduced by chemotherapy except for activated T cells and natural killer cells. The impact of selective modulation of functional T cells subsets during therapy for patients with multiple myeloma is an important parameter which needs to be addressed in the overall approach to these patients.