BMMC of 24 patients with MM were cultured at 1 × 10⁵cells/well in medium alone (standard medium with 10 U/mL IL-2) or in the presence of IPP (4 μmol/L) or pamidronate (4 μmol/L). In a significant proportion of patients (14 of 24 evaluable patients) an activation (up-regulation of CD25 expression) of BM-γδ T cells could be demonstrated by FACS analysis after 3 to 5 days in the presence of pamidronate. After 5 days of culture, the number of viable plasma cells was determined as described in “Materials and methods.” Results are expressed as percentage of plasma cells according to the following calculation: [plasma cell number in treated (IPP or pamidronate) cultures]/[plasma cell number in control cultures (medium alone)] × 100. Plasma cell percentages in each group represent mean ± SD of 24 (14) patients. The Student ttest was used to determine statistical significance of detected differences. P values refer to the comparison of the various groups with medium alone as control.