The simultaneous activity of multiple stimuli can be difficult to analyze, particularly on biological systems. However, these analyses are becoming increasingly important in drug or pesticide formulation for efficacy. This article will review techniques for the design and analysis of bioassays of mixtures. The two major techniques that will be reviewed are based upon the concepts of response and potency. Particular emphasis will be placed upon measuring levels of synergy, i.e., when the

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... is greater than the sum of its parts, and antagonism, i.e., when the activity is less than would be expected. Theoretical examples will be given to demonstrate the application of each technique. The method based on potency was used in the design and analysis of Dr. Gregory Armel's study of the differential response of atrazine mixtures with bleaching herbicides that target different sites in carotenoid biosynthesis. Examples from this mixture study are presented.