We have employed the asymmetric double cantilever beam (ADCB) specimen, which consists of a brittle adhesive bonding aluminium-alloy substrates, to measure the toughness, G~. We have investigated whether the ratio of the heights of the specimen arms (i.e. defined by the parameter A, where A = hi/h2) has any significant effect on the value of G~. We find no significant effects, and compare our results to those previously reported where a dramatic effect was found, but could not be explained.