An assembly of two receptor ligand bonds in series will typically break at the weaker complex upon application of an external force. The rupture site depends highly on the binding potentials of both bonds and on the loading rate of the applied force. A model is presented that allows simulations of force-induced rupture of bonds in series at a given force and loading rate based on the natural dissociation rates kR0,S0 and the potential width DeltaxR,S of the reference and sample bonds. The model is especially useful for the analysis of differential force assay experiments. This is illustrated by experiments on molecular force balances consisting of two 30-bp oligonucleotide duplexes where kR0,S0 and DeltaxR,S have been determined for different single nucleotide mismatches. Furthermore, prediction of the rupture site of two bonds in series is demonstrated for DNA duplexes in combination with streptavidin/biotin and anti-digoxigenin/digoxigenin, respectively.