Since its introduction, it has been recognized that the atomic force microscope (AFM) offers a unique ability to probe surface forces with nanometer resolution and that these surface forces play a vital role in the operation of the AFM (1). We (2, 3) and others (4, 5) have introduced a new approach to AFM in which a force is applied directly to an AFM tip using a magnetic field (MAC Mode AFM), rather than by pressing the tip into the sample with the scanning transducer. This method eliminates the spurious resonances seen in fluid tapping mode (3), leading to substantial improvements in image quality (6). Here, we discuss the application of MAC Mode AFM to the measurement of surface forces.