We measure the predictive accuracy of Internet-based product concept testing that incorporates virtual prototypes of new products. The method employs a two-factor conjoint analysis of prototypes and prices to enable a design team to select the best of several new concepts within a product category. Our results indicate that virtual prototypes on the Web provide nearly the same results as physcial prototypes. As virtual prototypes cost considerably less to build and test than their physical counterparts, design teams using Internet-based product concept research can afford to explore a much larger number of concepts. In short, the Web can help to reduce the uncertainty in a new product introductions by allowing more ideas to be concept tested in parallel.