A description for genotypic stability was developed based on the concept of a genotypic stability space. Environments were considered the measurement criteria. The coordinate position for a genotype was determined by the deviations of expected yield of the genotype from its yield if stable. An expression for the response of a stable genotype was developed. The relative genotypic stability measure was defined as the distance of a genotype from the center of the arrangement and presented as a measure of homeostasis. The comparative genotypic stability measure was defined as the distance between the positions of two genotypes and designed to measure the similarity of stability responses. The development permitted the testing of hypotheses with respect to stability concepts. A set of regional soybean test data was evaluated. The results for relative stability and the regression approach were comparable. Limitations for the regression approach were noted. Genotypes analyzed had different homeostatic properties. The genotypic responses to environmental stimuli appeared to be unique to genotypes and difficult to predict.