A magnetic force has been used to control a partially magnetized atomic force microscope cantilever in ultrahigh vacuum in order to investigate tip-surface interactions. It is shown that forces applied by an oscillating tip can drastically affect the measured response of the lever. In particular the oscillating force influences the measured tip-surface adhesion and can be treated as a simple addition to the static applied force in breaking adhesive bonds. Qualitative differences in force spectroscopy measurements due to the amplitude of the driving oscillation of the lever are presented and an alternative nonintrusive technique introduced. ©1997 American Institute of Physics.