The potential for the modification of the pharmacokinetics of doxorubicin (DOX) concurrently administered with high-dose verapamil (VER) has been investigated in 17 patients with advanced neoplasms refractory to drugs belonging to the multidrug resistance spectrum. Steady-state concentration of DOX, systemic clearance and urinary excretion were analysed. No significant difference was found between the kinetic parameters estimated for DOX at different levels of VER and those reported for doxorubicin as single agent. It can be concluded that VER does not appear to modify DOX kinetics.