Internationally, the high costs of pharmaceutical products limit access to treatment. The principle of differential pricing is that drug prices should vary according to some measure of affordability. How differential prices should be determined is, however, unclear. Here we describe a method whereby differential prices for essential drugs could be derived in countries of variable national wealth, and, using angiotensin-converting enzyme inhibitors provide an example of how the process might work. Indicative prices for drugs can be derived by cost-effectiveness analysis that incorporates a measure of national wealth. Such prices could be used internationally as a basis of differential price negotiations.