Abstract. This paper proposes the fitness control procedure for the application of genetic algorithms (GA) in pattern recognition. Instead of using GA to solve a concomitant optimization problem, the task is rather represented as a set of data bitstrings, and a similarity measure among those data bitstrings. Then, the GA is used to select the subgroup yielding highest mutual similarity. The paper also provides and discusses some examples for such a procedure, taken from the fields: pattern classification, clustering, and measuring.