In the present study 142 patients with myeloma (102 with IgG M-protein and 40 with IgA) treated with either VMCP (65 patients) or MMCP (77 patients) as remission induction therapy were retrospectively analyzed. Response to treatment was evaluated in terms of a more-than-50% fall of pretreatment M-protein and the posttreatment M-protein nadir. Though significantly more patients treated with MMCP achieved partial response (PR) as compared with those treated with VMCP (P=0.019) and though patients achieving PR showed a significantly longer survival than those with less responsiveness (P=0.0091), the difference in survival curves between the two treatment groups was not significant (P=0.1871). The difference in response between the treatment groups evaluated in terms of posttreatment nadir was not significant (P=0.507). Multivariate analysis identified posttreatment M-protein nadir as a significant prognostic factor associated with survival, along with 3 other factors: sex, performance status, and hemoglobin. The lack of difference between the survival curves for patients treated with the 2 regimens despite the significantly different response rates evaluated in terms of percent fall of pretreatment M-protein levels was considered to be due to the lack of a difference in the ability to induce a deep posttreatment nadir between the regimens. Posttreatment M-protein nadir is an important prognostic factor associated with survival and should be included in the evaluation of the efficacy of chemotherapy.