The design and construction of a 10 kg transportable flexure-strip beam balance to be used in searches of composition-dependent forces and/or tests of the weak equivalence principle is discussed. The results of the instrument performance presented herein are based upon operation of the balance under simulated experimental conditions that require our balance maintains a high level of sensitivity (i.e., resolution associated with the standard deviation of our data sample) during a continuous measurement process which alternates between two different elevations, a unique application for a beam-balance measuring device. Our results indicate that this balance is the most sensitive transportable balance used in measurement in the 10 kg load capacity range, obtaining a measurement sensitivity of about 15–20 &mgr;Gal. Also, we have established that our method of balance transport affects the sensitivity less than 15 &mgr;Gal at the 95&percent; confidence level. An increase in sensitivity of approximately 30 would be required to establish new upper limits on composition-dependent forces in the interaction range of most interest. ©1997 American Institute of Physics.