The quality-by-design concept is a new regulatory paradigm for pharmaceutical development, while the response surface method (RSM) is a promising approach for understanding design parameters for drug formulations. RSM aims to provide a visual image to support statistical design and analysis of experiments. However, neither contour plots nor 3D surface plots that have commonly been used can completely visualize interactions between the parameters within the design space, due to their limited dimensionality. This article presents a visualization technique that can simultaneously display the responses to multi-dimensional factors by mapping N-dimensional data onto unique x-y coordinates, re-defined by recursive slice-and-dice subdivision of the 2D plane. The applicability of the technique was confirmed using published data on the design of nasal drug formulations. (C) 2009 Elsevier Ltd. All rights reserved.