Modeling and visualizing molecular surfaces is an important and challenging task in bioinformatics. Such surfaces play an essential role in better understanding the chemical and physical properties of molecules. However, constructing and displaying molecular surfaces requires complex algorithms. In this article we introduce MetaMol, a new program that generates high-quality images in interactive time. In contrast with existing software that discretizes the surface with triangles or grids, our program is based on a GPU accelerated ray-casting algorithm that directly uses the piecewise-defined algebraic equation of the molecular skin surface. As a result, both better performances and higher quality are obtained.