The analysis by pulsed-field gel electrophoresis of partial digestion products visualized by probes for the human multidrug resistance (MDR) locus has been used to further establish the restriction map of this region. Results place the MDR1 and MDR2 genes on a single SfiI fragment, with partial digestion products establishing the distance between these genes to be 230-250 kb. The feasibility and potential advantages of using "natural" partials to generate detailed restriction maps within an amplified DNA domain are discussed.