A strategy for determining the most important components in a mixture system is developed. The proposed screening designs are usefrd in those situations where the number of candidate components,q, is large. Our simplex screening designs, which contain 2q+ 1 or 3q+ 1 points, are recommended when it is possible to experiment over the total composition range of all components (0–100%) or the experimental region can be expressed as a simplex in terms of pseudocomponents. We recommend extreme vertices screening designs, which contain approximatelyq+ 10 points, when some or all of the components are subject to upper and lower constraints. Examples are included to illustrate the proposed designs and associated analyses.