Randomization of program participants into control and experimental groups is often not feasible in field settings. The researcher's desire to evaluate a program with a rigorous experimental design is often incompatible with the objective of serving the expressed needs of the program participants. However, opportunities do arise when a randomized control group can be constructed without disregarding the participants' wish to be included in the treatment group. This article describes a method that uses the participants' compliance to program instructions as a means of classifying participants and, thereby, obtains a randomized control group for a subset of participants. A large smoking intervention project is used to illustrate two variations of this method.